Tony would be the "one-night stand"-turn-friend for me...
Bruce would be the long-time friend that I encourage in the dating scene...
Thor would just be the one-night stand to me after seeing his close-up in that Vacation red-band trailer...
Steve would just make me want Johnny Storm more than him... (No offense, Cap...)
Clint's married... so, he's a good-looking father in my book...
With all that said, I'm going to have to give it to Tony, but only slightly to both Bruce and Clint tying for second... If I was in a fourway with those three dudes, it would be the best-looking fourway I've ever been in... and ever will be in, in terms of Avengers swag... Other than that, sorry Thor... You're just not my type of best-looking Avenger, that's all...