I have no experience with Pimax/Deepon myself, so I can’t really comment on them. If I had to decide between Rift and Vive, well, I would have a hard time.
Vive’s “lighthouse” head tracking is easier to handle for larger play spaces, on the other hand the Oculus Touch controllers are better than the Vive wands: less clunky, more convenient and (important mostly for vorpX) a few more buttons.
Oculus Rift is lighter and has a better weight distribution, so most people will find it more comfortable to wear. On the other hand Vive has the softer ‘facial interface’ foam, which is also a comfort factor.
Vive has a slightly higher field of view, but Rift has a slighly less pixelated image (actually because of the FOV being a bit more narrow).
I could go on like that for a while. The point is: pros and cons cancel each other out one way or the other if you compare both headsets objectively, so in the end it comes down to personal preferences. Neither is perfect, but both are a great way to experience gaming like you never did before. Not too helpful for you to make a decision, sorry, but for me there ultimately is no winner (or loser) when comparing both.