Well, we've had a jolly old time ripping on our LEAST favorite characters, lets toss our favorite characters some props.
The only rule is you cannot list any of The Captains as your favorite character.
Even if they are your favorite. For example, my favorite character in all of Star Trek is Jean-Luc Picard, but that's too obvious an answer, so I'll go with my second favorite from TNG, which happens to be Guinan.
List your favorite character overall, or your favorite from each series, and give us a quick summary of the reasons you like that character.
I'll go first, in the "one from each series" format.
TOS: Bones, for his ability to the play the foil to Spock and his many, many memorable quotes. He seemed like one of the most well-developed characters in TOS, as well.
TNG: Guinan. I found myself glued to the screen whenever she made an appearance. A bit cliche? Maybe. But very enjoyable to watch and listen to nonetheless. Plus, Whoopie Goldberg has a very soothing voice that makes her fit the character profile even better.
DS9: Gotta be Quark. Both as a character who the writers weren't afraid to portray as a self-centered, profit-hungry b*stard, and as a character who slowly, over the course of the series, actually broke out of the Ferengi stereotype more times than one. Besides, unlike many of my peers, I thoroughly enjoyed the Ferengi episodes, which more often than not centered on Quark.
VOY: Tuvok. I didn't like him at first, but the more I watched, the more I realized that Tuvok is a delightful deconstruction of the typical Vulcan stereotype, much like Spock in his TOS movie and TNG appearances. Tuvok showed that the Vulcans really are a passionate species underneath that layer of cold logic, and I enjoyed his portrayal thoroughly.
I will go in Canon Chronological order...
ENT: Tucker. Despite a lack of character development, he was the absolute professional when it came to his engines. He was a good friend and even mentor to other bridge officers (Hoshi).
TOS: Sulu. Oddly, one of the best developed of the secondary characters. He had many hobbies, was well read, and was also absolutely focused on the job when he was most needed.
TNG: Reg Barclay. Great sense of humor. Developed fantasy life. Also a brilliant engineer despite his problems. Plus, he got turned into a spider!
DS9: Gonna have to go with Rom. Smart enough to know when to tell his brother to get bent and join the crew.
VOY: The Doctor. The most consistently evolving character and oddly the one with the most overt flaws. I was watching "The Swarm" the other day when he degerates like an Alzheimer victim. He is really brilliant.
TOS - Bones, for being a slight racist in a utopian and tolerant time and saying cool stuff like 'god damn it jim, im a doctor not a....'
TNG - Data , one of the all time great characters in TV. I honestly dont think any actor could have done a better job than brent. perfect combination of sci-fi, the search for the human spirit, comedy, everything.
DS9 - Garak, for having awesome lines and never truly knowing who he was or what side he was on
VOG- The doctor, probably the best of a bad bunch. went a bit weak toward the end but some of the stuff in the first 2 or 3 season were gold
ENT - Phlox - really the best in a bad bunch.
Overall i would say Garak, just for the huge range of quotes.
Odo - 'you'd shoot a man in the back'
Garak - 'oh its the safest way'
ToS : Scotty (I am biased here)
ToS Movies: Khan from STII; Gen. Chang from STVI (Klingons who quote Shakespeare are f*kin awesome)
TNG: Riker (in the later episodes and the movies, with beard and attitude to go with it)
DS9: Worf (as Capt. of the Defiant)
VOY: Holographic Doc; 7 of 9