I think Kirk was the best.
Captain/Admiral/Captain Kirk was the first so every Captain after him gets compared to him. He got the job done always, he was charismatic, could manage diplomacy (barely), was innovative and clever, and knew when to take off the gloves and go in swinging. He got promoted to Admiral, although it's hard to tell how many stars he had (the insignia does look like a diamond suggesting 4 stars-- Full-Admirals currently on their shoulder boards four stars which are arranged like a diamond with the final star trailing a little bit further behind than the others). In ST: TMP, his insignia was that of a Rear Admiral (a 2-inch broad stripe with a half-inch stripe above it), but that took place 13 to 14 years before Star Trek II. Star Trek II, III, IV, and V take place only a few months apart (ST II = 2284-2285, STIII 2285 3 months after II, STIV a few weeks to months after III, and STV, just a few days to weeks after IV).
Captain Picard: Picard may have been the best Captain for a peacetime scenario (although all of the ST: Universe was peacetime except some of DS9). He was smooth and knew how to use diplomacy and could usually talk his way out of a fight. He commanded a ship that was a cross-between a battleship and a cruise-liner so that may have been his motivation for avoiding fights, but still. Diplomacy's good in real life, but it has little place in a Sci-Fi story. I think he basically was a wuss. He does have a powerful authoritative voice, which makes him sound very believable as a ship-captain. He can fight quite well though actually, so he's not entirely a wuss. But he does take a bit longer to take off the gloves than Kirk, or Janeway. To be honest, I would have prefered if Riker was the captain in The Next Generation rather than Picard, he was younger (35 in 1987-- same as Kirk was back in 1966), tougher, and he really knew how to put up a fight.
Commander/Captain Benjamin Sisko: Sisko was okay, and was probably the only officer in the fleet who knew how to really cook! He was also the only black-captain with a major role in ST (There was a captain in ST: TNG who was a black woman actually, but she had a small part only). He was the only captain in ST who was spiritual. Kirk was pretty much an atheist or at least heavy agnostic, Picard seemed more agnostic, Janeway... no idea, probably somewhere in the middle (agnostic). Sisko had a definite spiritual leaning (the prophets-- hey, a prayer made an entire Dominion fleet DISAPPEAR!!!) He was okay when it came to most things on a station, but really was at his best when it came to duking it out in space on the USS Defiant. Now that's a ship!!! DS9 was the only series that took place during a war (some of the movies took place during the same time, but still... I'm talking about series) He looked much tougher when he did away with that wussy short hair and shaved it bald. He also has a good powerful voice too.
Captain Janeway: Now Janeway I liked! She's like a female Captain Kirk... doesn't look as good though, but she's clever, she can do diplomacy (I think she may be even worse than Kirk!) and she really can kick ass and take names when it counts. She's probably not so good in a bar-room brawl as Captain Kirk though, about the same behind the controls of a ship (maybe a little less). She's also the second Star Trek Captain to end up as an Admiral (Kirk was the first). She also had a low-pitched voice which was a good thing... made her sound quite tough. Even though her voice was that of a 55 year old when she was only 39 (series started in 1994, and she was born in 1955).
-Concordia