Well...
From TOS:
I think it would be Spock. Simply because of all the 'Logical' ****
- I don't really remember TOS all that well. Haven't watched it in a long time.
From TNG:
For this one, I'm going with Worf. Simply because he is a Klingon, and whilst he does his job as a Starfleet Officer, he still goes about certain things in a more Klingon approach.
From DS9:
I think Jadzia Dax (cuz she's hawt)
Nah, seriously, she played her part well.
From VOY:
I'm going to have to go with The Doctor. Message in a Bottle was such an awesome episode, and it wouldn't have worked without the Doctor. Along with him, Kes. She was new, young, and willing to learn etc.
From ENT:
I think I am going to have to share the first view, of which is Trip. He did his job, and his role well.
In addition, other characters (reoccurring) I think I'd have to put Gowron, Martok & Damar. All from DS9 (though Gowron was in TNG too), but you got to 'know him' more in DS9.