---TL;DR ---

Quest 3 is probably your best bet if you don't know what you're looking for.
Index is going to be the easiest way to get FBT and lighthouse tracking, but the resolution and lenses are a bit dated for the price.
Quest 3S is likely to be your best budget option at this point.
Quest Pro is still the most common option for people that want face/eye tracking at this point, but it has been discontinued. Software support may become an issue in the future, so keep that in mind if you're considering it.

Expect to spend extra money on a better headstrap if you pick up a Quest 3 or 3S, and a dedicated router for wireless at some point if you pick up any of the Quest headsets.

--- PC REQUIREMENTS ---

Aside from just looking bad, not being able to maintain a smooth framerate in VR can actually make you feel sick, so it's important to make sure your PC is up to par.

The SteamVR Performance Test is pretty out of date, but it's a good way to see if your PC is way too weak for VR.
There's a similar check for the Index here, but that's also a bit out of date at this point.
The SteamVR Performance Test has been delisted, and the Index test just checks to see if your hardware meets the listed requirements. For now, checking requirements on the games you're interested in and asking around in the thread are going to be better options. Keep in mind that higher resolution headsets will require higher GPU performance.

If you're looking to upgrade or build a new PC for VR, Logical Increments is a good place to start since they have a guide specifically for VR builds.
There are some VRChat specific details available here as well.

If you've got any questions, post in the thread, and we'll try to help.

--- CURRENT HEADSETS ---

Quest 3 is smaller and lighter than the Quest 2, with pancake lenses and a higher resolution screen. Resolution is higher than the Index, but loses out to the Beyond. The sweet spot is much larger than either of those, and the the FoV is about on par with the Beyond. Updated SoC gives better performance in standalone games and allows for AV1 decoding when using it as a PCVR headset assuming your GPU supports that. Passthrough cameras are much clearer than the Quest 2 and Quest Pro and give you a color view of your surroundings, they're good enough to be usable for some AR/MR applications. Controllers aren't self-tracked like the Quest Pro, although it's possible to use Quest Pro controllers with it. The controllers are similar to the Quest 2 ones without the rings, which makes it slightly easier to occlude a controller and temporarily lose tracking. Tracking cameras have been moved, so tracking volume is better below the headset and worse everywhere else. Built-in audio is mediocre, built-in mic is worse than the Quest 2 and significantly worse than the Index or Beyond. Stock head strap is uncomfortable, although this can be fixed with the official Elite strap or a number of 3rd party ones. Can be used as a PCVR headset either wired through Link or wirelessly through Air Link, Steam Link, or the Quest native version of Virtual Desktop. If you're autistic about latency/compression, be aware that any method for using a Quest with a PC will have at least a little bit of both, although it's not generally noticeable on an ideal setup. Also worth mentioning that Quest headsets give you access to a few exclusives that currently aren't playable any other way, although they do have to be played standalone. Still requires a smartphone and a Meta account to set up, and telemetry is harder to block now.

The Valve Index is still arguably the best overall PCVR headset kit out of the box, although depending on your use case and willingness to mod or piece together a hybrid setup, there are likely better options. Unlike most of the current alternatives, it still uses lighthouse tracking instead of relying on headset cameras and allows for easy integration of full body tracking. Still has the best built-in audio and microphone, and the FoV and refresh rate are still good. Visuals aren't as good as the more recent headsets, with resolution, color, and black levels being much better on the Bigscreen Beyond and sweet spot and resolution being better on Quest 3. Comfort is better than the Quest headsets are out of the box, but loses out to the Beyond. Controllers and cables do tend to have some durability issues, although the controllers are currently much better than the launch version.

Bigscreen Beyond is a lightweight, high resolution SteamVR headset with custom molded face gaskets. Uses lighthouse tracking, so you can reuse any compatible controllers and base stations if you're upgrading. Much smaller and more comfortable than the other options out there right now. Great resolution and great colors/contrast with the microOLED screen. Slightly lower FoV than Index, with a lower refresh rate (75Hz/90Hz) and smaller sweet spot. No built-in audio, but the built-in mic is on par with the Index mic. Requires a face scan from an iPhone for the face gasket, although it's quick enough that you can borrow one or use one at a store. Not generally recommended for someone new to VR because of headset price plus separate controllers and base stations, but it's a good upgrade from another SteamVR headset if you're fine with the tradeoffs.
Full review from an anon here: https://rentry.org/6stwcu

Pico 4 can also be good budget option if it's easily available in your country. Loses out to the Quest 3 and Quest Pro, but it beats out the Quest 2 in specs, so if the price is low enough, it's a good alternative to that. Like a Quest, it can be used as a standalone headset or connected to a PC either wired and wireless through Streaming Assistant or Virtual Desktop to play PCVR games. Same latency/compression disclaimer as the Quest applies here too. Has pancake lenses like the Quest 3 and Pro, which are an improvement over what's available in the Quest 2, but has a significantly worse game selection if you're using it as a standalone headset. Built-in audio is disappointing, so you'll probably want to rig up some kind of external audio setup, which is slightly more difficult than a Quest since there's no 3.5mm audio jack.

Pico 4 Pro adds face and eye tracking to the regular Pico 4, but is otherwise basically the same headset. Face and eye tracking also require you to use the Chinese firmware instead of global, which means you're stuck with Pico's official Streaming Assistant instead of Virtual Desktop. Notable mostly for being the cheapest way to get face and eye tracking if it's available in your country, but hard to recommend for most people.
Review from an anon here: https://rentry.org/tsewbomu
Setup guide here: https://rentry.org/2h3edfdp

PSVR 2, while better than the original, still has a fairly limited selection compared to PCVR or a standalone Quest and is pretty hard to recommend. Sony is working on some form of PC support at this time, but it's not clear exactly how it will work and what functionality will work on PC.

--- UPCOMING HEADSETS ---

Quest 3S is rolling out now, it's basically a Quest 2 with the upgraded SoC from the Quest 3. Won't make much of a difference for PCVR use, but it'll be better than a Quest 2 for standalone games.

Pimax has announced the Crystal Light and Crystal Super, both PCVR only headsets.

Depending on which rumors you believe, Pico 5 has either been cancelled or completely reworked, and Bytedance is also supposedly working on a Vision Pro competitor.

Quest Pro 2 is supposedly coming in the first half of 2025 has been delayed due to disagreements between LG and Meta, and may be as far out as 2027.

--- DISCONTINUED HEADSETS ---

Quest Pro falls into a weird middle ground between the Quest 2 and Quest 3 in most ways with a few unique features that you can't get on either. Weight and screen resolution both fall between the Quest 2 and Quest 3, although it does have pancake lenses like the Quest 3 that allow for a better sweet spot. The SoC is shared with the Quest 2, but clocked slightly higher which helps a little with standalone games, although it's still far behind the Quest 3. The mini LED screen on the Quest Pro allows for better color and uses local dimming to improve black levels, although it still loses out on clarity to the Quest 3 due to lower resolution. Comfort is better than the Quest 3 out of the box. It also has face and eye tracking that can be used in VRChat and in some cases for foveated rendering. Includes self tracked controllers that can be bought separately to use with other Quest headsets, and a dock that's a separate purchase with the Quest 3. It's not generally better for games than a Quest 2, and loses out in clarity and weight to a Quest 3. However if face and eye tracking are a must have for you or you really want the Pro controllers, it can be worth the extra money, especially if you can find it for cheaper than MSRP.

The Quest 2 can still be a decent budget option if you can find a good enough deal on one. Quest 3 has a significant advantage in visuals and the updated SoC in both the 3 and 3S will be much better for standalone if you care about that, but it'll still work fine for PCVR and most standalone use. It has been discontinued as of Sept 25th, 2024, so expect to see support phased out over time like it was for the original Quest.

Reverb G2 is still decent for sims if you can find it cheap enough, although with WMR support being dropped, you're better off looking into other options. Headset resolution is high, but the controller tracking, while still usable, is subpar compared to other headsets. Playing some heavier SteamVR games through the WMR software can add some overhead, OpenComposite can help if you're running into performance issues there.

Older headsets like the Vive, Rift CV1, or Rift S are only worth picking up if you can find one very cheap. WMR headsets are generally not recommended at this point.

--- ADDITIONAL RESOURCES ---

Updated Space Calibrator fork for hybrid setups:
https://github.com/hyblocker/OpenVR-SpaceCalibrator/releases

OVR Lighthouse Manager (base station power control for hybrid setups)
https://github.com/kurotu/OVR-Lighthouse-Manager/

Old Oculus Rift Setup Guide:
https://pastebin.com/QgHwLq8R

Old HTC Vive Setup Guide:
https://pastebin.com/QNc18zHd

Wiki with some details for running on Linux:
https://lvra.gitlab.io/

Compatibility List for Linux:
https://db.vronlinux.org/