Always a tough question. TOS, while dated, is the primer. I grew up as TNG was airing. It’s janky and problematic until about the 3rd season. DS9 is the best of the best as far as I’m concerned, but it’s a slow burn to build the characters and get to the meat of the arching story. Of course, there’s a chronological approach, however, kinda messy.

Try out one for a few episodes, see what strikes your fancy.