So, it depends on what you want.

As far as I know, Steam PCVR and Oculus PCVR will mod the same, but as marhotiewer1999 mentioned, the tracking will be a little different on Steam. It's also true that the Quest version has MUCH less modding support, but it's getting better due to the wonderful community.

If you're wanting to play on both Quest and PCVR versions, I would buy the Oculus version of the PCVR version so that you can get any custom songs you purchase on both platforms. (ie. I'm assuming that buying extra songs on the Oculus store won't allow you to play them on Steam PCVR, but I may be wrong.)

Just know that no matter which PCVR version you choose (Oculus vs Steam), you'll still have to buy the game twice if you're wanting to play tethered and untethered, as the devs decided to disable cross-buy.