Well it's not like they don't all have problems of their own. (spiderman did lead iron man , storm , captain america, ff and black cat in the 90's animated series) the top 5 are probably:
spidey
iron man
captain america
Wolverine
hulk.
Also you ppl haven't thought of females have you:
top 5 females
elektra
black widow
jean grey
rogue
black cat
anyone dissagree?
I'm going with 'leaders' from a more tactical standpoint.
Captain America, first and foremost
Cyclops
Cable
Dr. Strange, leading a misfit band of heroes such as the Defenders takes talent
Baron Helmut Zemo, seems to be doing a good job with the Thunderbolts
Honorable mentions:
Storm
U.S. Agent (I just think he's cool anyways)
Angel/Archangel (back with the Champions, not going insane while trying to govern such a ragtag team as that is an accomplishment)
Hawkeye
Pete Wisdom