Angel by far, simply due to motive.
 
Bubbles, being a cat, has a cat’s self-confidence and sense of entitlement. He’s just an asshole on general principle. He has no motivation take it any further, because there’s nothing personal about it.
 
Angel, being a bunny, is on the business end of the food-chain, and knows it. That deeply hidden fear gives him a BIG motivation to be an asshole toward anything that could conceivably be a threat to him. Unlike Bubbles, to him, it’s personal.

The word is “competition”, OP. Competition is “an activity to strive to gain or win something by defeating or establishing superiority over others who are trying to do the same.”
 
“Competence” means “having the necessary ability, knowledge, or skill to do something successfully.”

Angel is cuter and more devious. Not to mention more successful IMO.

@Beau Skunky  
Angel’ll pwn that pfeffa utterly.

I wanna see them fight.

Bubbles, definitely. Angel has a heart of gold, while Bubbles is a plot through and through.