I found Seven to be the most interesting character, by a wide margin. Actually, as analytic/not fully human characters go, I preferred her to other shows' versions, including Trekkie uberheroes Spock & Data. The Spock resisting his human half bit, and Data trying to learn to be human spiel, so often was forced and obvious. Whereas with Seven, we weren't hit over the head with moral lessons -- she was an often pissed-off former Borg, learning (very gradually!) how to adjust to a new existence. The writers really treated that character well, and forget the sex bunny stuff, Jeri Ryan was terrific in the role. I have no idea if she can play any other character, but she sure was born to play Seven.
The Doctor was my favorite Trek doctor, as well.
Torres was interesting, it was usually fun when she was on the screen.
Janeway was OK because the captain gets a lot of attention, but to my mind her character was the dullest and most poorly written captain except for Archer.
As for the rest, Tuvok was underused. Chakotay, OK. Paris & Kim, ouch. Neelix, not to my taste.