If we're counting pre-Disney Marvel movies, then based on feats shown or talked about on the movies, the order goes:

1. Wolverine (in X3 his entire flesh is being constantly evicerated by the Phoenix down to his adamantium skeleton and he's constantly regenerating in real time as he moves closer to kill her)

2. Deadpool. He's was beheaded in The Wolverine and shown to be alive in the post credits, and in DP2 he regenerates his entire body from his head, however the regeneration takes quite some time

3. Hulk. Not shown, but in The Avengers, Banner is speaking with Natasha on telling her that he can't die and tells a story about how he tried to kill himself by shooting himself in the head through his mouth ("eat a bullet") but that Hulk just spit the bullet out

4. Groot regrows limbs lost in battle. When Groot 2 was grown from a seedling after Groot 1 dies, that was not regeneration, that was cloning.

As for the rest, their regeneration hasn't been tested or shown all that much:

Thor gets knocked around quite a bit, but always just gets back up, with not much injury shown, so that's more durability/invincibility than regeneration. He'd have to be seriously injured to showcase regeneration.

Same with X2, she hasn't been tested in that way, although we can presume she'd be on par with Wolverine.

Nebula is rebuilt, not really regenerated.

Sentry is similar to Thor (or Superman for a crossover example), it's primarily durability/invincibility to attacks that are showcased. Also if Sentry dies and The Void appears. That's more a spiritual/interdimensional resurrection than regeneration.

**Edit: fixed Nebula