I'm inclined to say U-Thor, as he went toe-2-toe with an utterly enraged Ultimate Hulk, while Caiera went up against a still weakened Hulk when they faced off.
She's very skilled and durable enough to take hits from Hulk. But the fire-bomb isn't her best showing, she tanked flames(heat) and we're lead to believe Hulk was KO'd by the fires cos he was affected/fighting the spike-virus already.
By an utterly enraged U-Hulk who also took out all the Avengers, after he took out the Chitauri.
Caiera was doing well but losing to a weakened Hulk before the fight stopped due to the spikes and her fleeing. Butthurt U-Hulk would have slaughtered her.
Thor was doing well but ultimately lost to a much more powerful Hulk.