i love when guys wear Neutral colors. black, white, gray, blue with Jeans and some converses/or vans to complete the outfit. Its Simple yet stylish. I'll focus on your features more (arms, eyes, hair) rather then the yellow or baby pink polo shirt your wearing. I saw some kid with some neon green pants the other day it was...interesting to say the least. He was cute but I couldn't get over the pants!
Well if the guys in decent shape, I think slim tees(form fitting shirts) look really hot! I also think guys look really handsome in suits (think James Bond) and other formal attire. Also career attire can be hot, such as firemen, policemen, men in the military, etc.
Personally, As long as it's not to big and not falling off you; definitely not a stereotypical nerd outfit either though. Other than that it really doesn't matter as much. As long as you work what you've got.