"Star Trek" - I pretty much like all of them. People call some of the main cast underdeveloped and too cliche, but they were all good enough for me.
The one character I'd describe that way, to the point where it rubbed me the wrong way, was the Nurse. She wasn't much of a character and didn't do much, but I found her crush on Spock a bit corny. She didn't seem like a very useful character, existing only to give the actress a role and add some unnecessary (and unconvincing) melodrama to some Spock crises.
"Star Trek: The Next Generation" - Troi, Tasha, Pulaski, Wesley, Lwaxanna Troi, and Geordi. Some of those have their moments, though. I liked a few episodes centered around Wes and Geordi. Pulaski was cool in "Peak Performance", Tasha was great in "Yesterday's Enterprise", and I enjoyed Troi's big scene in "Star Trek: First Contact".
"Star Trek: Deep Space Nine" - I hated Kira for about three seasons and kept wishing she'd be killed off, but she got better later.
I hated Odo for awhile, too. His gravelly voice and constant bullying of Quark irritated me, but when I really despised him was when he let the female Changeling manipulate him into having a superiority complex over humans, to the point where he stood idly by while his friends' lives were in danger. I know he was torn between his friends and family, but I had no sympathy for his identity crisis. Once he and Kira were together, I liked them both more.
I generally like the main cast here, but some of the recurring characters got on my nerves, particularly Ferengi and Bajorans. Kai Winn and Opaka were both insufferably preachy. Vedek Bariel and Shakaar were unbelievably dull (until Odo, Kira's boyfriends were even more bland and grating than she was).
The only Bajorans I always liked were Leeta and the one that killed herself in protest. I liked most of the Ferengi characters, but Rom, Zek, and Ishka had the most shrill, agonizingly unfunny 'wacky' voices that made me cringe every time they spoke. Rom had some admirable bravery and smarts, but his body language and voice made him unbearable to watch. Zek and Ishka were just lame in every way.
"Star Trek: Voyager" - I hate pretty much all of them except Janeway because I find her attractive and Tuvok because he reminds me of Spock.
"Star Trek: Enterprise" - I like all of them, although Doctor Phlox's manner (i.e. the way he talks) can be annoying at times.