Half seriously, I would have to say Jean Luc Picard, because he apparently had some sort of multiple personality syndrome. When I was first introduced to him, he was a cold, reserved administrator who stayed on the ship as befitting his rank. By the time he was done, he was a goddamn action figure who was constantly saving the Federation in his undershirt and doing the samba in his spare time.
I have to agree with you, but he was even less worthy of the captain's chair than that. In the first season he surrendered the ship to any Ferengi who happened to be in the quadrant. Who knows how many cans of Turtle Wax were needed to keep his noggin shining bright?
Kirk was such a good character that TNG split him in two. The captain part went to Picard. The likable adventurer went to Riker. Then Patrick Stewart started complaining that "Shatner got all the babes. Why don't I get any babes?'
That was during the crossover two-parter called "The Best of Both Worlds." When they finally worked out Stewart 's contract, he got to hold onto the center seat while Riker was emasculated. Just once I with they'd have had Riker read the opening monologue to see how many people would pass out because it wasn't Picard.