Like several folks in this thread, I started with TOS reruns in the 70s. The original series is still my favorite with TNG second.
Something is compelling about the interplay between Kirk, Spock, and McCoy. All later series had more of an ensemble cast, lacking that particular TOS dynamic. I also prefer the emphasis on exploring space that later ship-based series didn't use to that degree and also that TNG largely abandoned in later seasons
I sampled VOY, DS9, and ENT when they came out but quickly lost interest in them all. Within the last several years I have watched all three of those series and while I enjoyed them all in different ways, they will never approach TOS and TNG for me. I know people rave about about DS9 in particular but I just don't hold it in that high regard. Maybe it's because I didn't watch it in the first run, I don't know.
For new shows, I've only seen the first season of SNW and enjoyed it greatly. The Kelvin movies, while fun as a lark, are forgettable for me.