Regarding Picard as a leader...
He has great traits that work in his favor. (Excellent diplomat, highly ethical, one of the biggest champions of personal freedom, and a few others.) But I wouldn't want to serve under him.
Why?
Because he's not really approachable. Outside his senior staff, he is almost completely closed off from the crew. One of the traits of good leadership, in my experience, is approachability. If you have a leader who is not, you never want to go to them when a problem is occurring.
This is one of the areas where Sisko really shines. He's very approachable on a regular basis. He'll take Emissary requests while he's in Quark's having a drink ("ACCESSION"), he'll take a few minutes to talk with people on the Promenade (a distraught Rom in "FERENGI LOVE SONGS", agreeing to marry Leeta and Rom in "CALL TO ARMS", talking to children in various episodes, etc.), he cooks for his officers (multiple episodes)... he's very much a leader who understands the value of keeping his crew happy.
(In the end of "RULES OF ENGAGEMENT", Sisko explains to Worf how being a leader is knowing when to smile for your crew even if it's the last thing you want to do.)