Bashir (quirky, socially inept, eager, intelligent... naive... when doing my DS9 rewatch and seeing season 1 again for the very first time, Bashir was one of the most refreshing characters, especially when placed next to Kira... he had a great arc over the span of 7 years, though I don't recall the eugenics stuff as much as I should be, I only remember thinking of how all that conflicted with Khan and all that (at the time)...)
Pulaski (not a mere "McCoy clone", which other Trek doctors would end up emulating from a template, she knew modern methods and memorized older techniques as a standby should the technology fail. Not only no-nonsense, she even knew of antidotes and vaccines, allowing her to partake in Klingon rituals because she was fascinated by Klingon society. Wish she had stayed, Pulaski added a lot more than Crusher had, IMHO. )
EMH (Picardo is great but the EMH is too often a McCoy clone, then comes the shoehorning redo of "Measure of a Man" but applied to computer generated images instead... on the plus side, two words raise the ante for him considerably: "Living Witness". Episodes where the EMH gets to do stuff make up for the McCoyisms and, again, Picardo often steals the show. That and maybe the EMH's creator had taken aspects of medical officers for use in his EMH template. McCoy being a prime candidate of study. I can dig it.)
McCoy (the original for others to emulate, yes, but some of his comments can be a bit too racist against Vulcans at times, going beyond good-natured politically incorrect ribbing at Spock, but YMMV. The two did have a camaraderie despite their sparring, and Spock too made anti-human comments at times. Just not as often.)
Crusher (At least she wasn't a blatant McCoy clone ;season 1 TNG is laudable in trying not to copycat character tropes from TOS. She was more fun when she had red hair, but later seasons often only use her as a preaching prop - if she had anything to do at all... the orgasm episode is very early-90s, since Marcie Rhodes was going it on television as well. "Star Trek TNG", meet "Married with Children"...)
Haven't seen enough of ENT to place Phlox anywhere yet.
Honorable mention, would have been nice to see more of him in TOS' run:
M'Benga - Booker Bradshaw makes Dr. M'Benga his own, despite having very few episodes to be in, leaving the audience in wanting more.
http://memory-alpha.wikia.com/wiki/M'Benga