I would guess most people's trek would be the Trek they saw first, or at least, in a formative period of their life. It is for me, at least.
For example, I've never really been able to get into TOS. It's from an era before I was born (1973) ; an era therefore with role patterns essentially alien to me. Too 'cowboy' style for this European. Scenes are spun out too long, too hammy and 'dramatic' sometimes for my tastes. Many concepts that are trivial now must have been revolutionary back then, but I can't see them with a fresh eye. In short, I can't really enjoy it when I watch it -and I've tried many times-, even though I can recognise its quality.
Grew up with TNG. Initially my favorite series, in retrospect I think it is a bit bland; too upright and limited.
I guess DS9 is my Star Trek. Much in the same vein as TNG, but without the limitations I listed there.
Voyager: Sometimes enjoyable, healthy dose of humor, but also with serious issues. Lacking on character development and focusing too much on the 'big three' in later years. In the earlier years they at least tried to be original, and I regret they dropped so many issues (resource scarcity, conflict between the crews) from that era so easily.
ENT: mixed bag. I liked seeing an 22nd Alpha Quadrant very different from the 'federation home quadrant'. Season 1 and 2 were perhaps too episodic and 'light' (would have liked to see more on earth's political development and the situation leading up to the foundation of the Federation), and perhaps Season 3 was too 'heavy' (all that expanse stuff going on without many 'lighter' episodes in between). I think season 4 struck the balance just right - when we really started seeing developments that would lead to the formation of the Federation. Regrettably, it was canceled at that point, just as the series started to become good.
DIS: I enjoyed the seasons I saw, as a series in its own right. Still have difficulty fitting it into the Trek framework, however.
PIC: have only seen one season and it was too dystopian for me. However, only having seen that one season, I'd like to suspend judgement for now.
Haven't seen the remaining series.