X-Men? Fantastic Four? Avengers? Justice League of America? Legion of Superheroes? Discuss.
The Mighty Heroes:
Strong Man
Diaper Man
Tornado Man
Rope Man
and Cuckoo Man
Power Pack
Legion of Superheroes, Silver Age incarnation.
damn you for stealing my thunder!!!
The Fantastic Four, most preferably the Lee-Kirby, Marv Wolfman, and John Byrne creative runs.
Second behind the FF would have to be the Midnight Sons (formed by the Ghost Riders, and also featuring Dr. Strange, Blade, Werewolf By Night, Hellstorm, and Morbius among others) with my being a sucker for all things supernatural and Halloween. (And I’d still be if Halloween didn’t happen to be my birthday. 
)
Blame Tornado Man
“I’m thirty seven years old! I’m plastic training pants man!”
I’m kinda fond of Squadron Supreme, the 12-person team that’s a rough clone of the Justice League of America.
I loved the Justice League Europe comic book; those were some of the funniest funny books ever!
But I’m going to vote for professor Gina Diggers graduate students, with Prof. Diggers and her sister along to keep things from going wrong (haw!) “Gold Digger” is my Numbah One fave comic book. (“Agency Zero” is also a lot of fun, as is the “World Explorers’ Society.” But it’s when the grad students break open another ancient tomb of unknown horrors that the going really gets fun!)
ETA: Marvel had something of vague promise with The Illuminati, a group of six or seven of their heaviest hitters…even if they were all white men. The stories didn’t live up to the promise, alas.
Superman and Batman, when they’re not doing something stupid like fighting each other for no reason. Basically the early-1980s World Finest pairing.
Aye; it’s no contest at all: the Mighty Heroes win!
Dude, clearly it’s just that great minds think alike.
Captain Carrot and his Amazing Zoo Crew
Mystery Men
One of the Illuminati was(and may still be, should they ever get back together)
a certain T’Challa alias the Black Panther…
Doom Patrol.
Their name alone makes them number one. It’s pure poetry.
The Incredibles
Nextwave.
Although I’m not sure there is a distinction to be made there between the team and the book itself, since it only ran like twelve issues and was never revisited. My frustration with most team books is that the roster changes so often that it is impossible to follow a single team over multiple stories. Most writers just assemble the team they want for that particular story, and then the next writer reshuffles the deck for the next story arc. Only a very small number of teams, like the FF, have been at all consistent over the years.
Birds of Prey. Closely followed by Runaways. Then The Authority.
Chris Claremont X-Men up to issue 200, or a little earlier.
As a kid: The X-Men
As a Grown-Up: The Watchmen
As a Dad of Young Kids: The Powerpuff Girls
As a Dad of older kids: The Incredibles
X-men all the way.
They’re what got me into paying any attention to the comic book world, so they will always be my favorite.