My favorite is J. T. Esteban, because he was so dependable Starfleet trusted him (over Kirk who had more reasons to do it! he was there and saw everything, andhad the Marcuses+Saavik already onboard) with the most controverted mission of the galaxy (too bad his ship took a "lucky shot", but at least he never had a shrink and a kid in his bridge, was not abducted by a deity from a wormhole, never got lost in the other side of the galaxy and didnt have to found his own version of Starfleet just because the one he had wasn't good enough)
My least favorite is Captain Spock. If he had done his job properly when Kirk asked for a place where to deposit Khan (what about "The planet Ceti Alpha 5 can support life BUT further analysis show the planet 6 will explode in aprox. 6 months and lay waste to 5"? then Kirk would just say "let's find another planet then" and a lot of pain would be spared for everyone. Such science officer....).
The green-blooded hobgoblin deserved the radiation poisoning he got.
As if all that wasn't enough, he CAME BACK FROM THE DEAD, ponfarred his first supposedly protegé, mind-raped the next (and SHE was arrested!), went to Romulus, made friends there including kids, then let the ENTIRE PLANET be destroyed by a supernova, in the process causing an entire screwed timeline to form where his home planet also bought it and Kirk picks fights at bars. Now he is dating Uhura, and I bet he didnt tell the poor girl his zombie self probably impregnated the half Romulan girl but it's alright because he left her on Vulcan to be sucked by a black hole. Ugh. Won't he never stop?