There are so many to like. But, in a random order, I'll go with Hulk (any Hulk), Colossus, Spider-Man, Thor and Mr. Fantastic.
Others: dr. Strange, Juggernaut, Namor, Wolverine, Thanos, Venom, Black Panther and even the grandiloquent Gladiator (somebody has to like him).
And when I was young and foolish, I had some kind of crush on Rahne Sinclair. She looked so cute back then...
And no, not Gambit, I know most people adore him, but I'm not too crazy about him 馃檪.
Captain Marvel, Genis is pretty cool, especially after going insane, he does the most crazy shit and it makes some good stories.
Scarlet Spider, (duh) something about clones and imitations (ala U.S.Agent) always seem cool, to me at least. You get to see the same powers, but with a different persona controling them, and sometimes some cool and weird stuff happens.
The Slingers too, that was a good team that they should do more with. Bring back the Slingers. And the good Green Goblin.
And most recently Kasper Cole, the White Tiger, I hope to see him a lot if they do another Panther series, or feature Panther in something, which I heard some faint rumors of a new series. T'would be cool.
And the Thunderbolts are awesome, along with the Inhumans, Invaders, Maverick, Deadpool, and the Taskmaster. etc. etc.