For me it has to be the green arrow, his outfit speaks for itself really, very traditional Robin Hood design, and being English that really appeals to me and my childhood.
He also has a great sense of humour, Kevin Smith was great choice as a writer for the new series.
As I already stated to being partial towards Green Lantern in another thread, I still have to say I like the Green Lantern Costumes. They are stylish but still have their individuality since each Green Lantern can make...or remake their costume at will. Although the outfit that Guy Garner wore for ages ( with the large white moon booties ) had to be my least fave Green Lantern outfit.
But Green Lanterns get it all...a nice domino Mask ( optional )......form fitting costume using green and black ( usually ), nice bling...( jade colored ring), plus they never need to be dry cleaned! hahahaha.
In the more..."down-to-earth" heros, I would have to choose a lesser known character named Kevin Matchstick, from the Comico publication, 'The Hero Discovered --- Mage"
He wore a black short sleeve t-shirt with the 'shazam' type yellow thunderbolt on the chest, a pair of Levis, and usually sneakers or docksider shoes. Add that to his glowing baseball bat, and he was high up on the ..."street cool" charts, to me.
For my favorite costume, I would have to give it to the Punisher. His "costume" is the closest you can get to jeans and a T-shirt in the superhero world. Also in at a close second, Dr. Strange, with all the baggy, mystical attire, he doesn't look menacing or fierce, but one look at him leaves no doubt that he has power beyond reckoning.