I know almost nothing about fashion, but here's my two cents, heh heh...: Go bold. Get one of those slick "chalk" pinstripe suits with the big old fatty pinstripes, 3-button if you're thin, and 3-piece if you can find one (versatile). For some reason I think a 3-piece looks real sharp if you're young and thin and can pull it off. I have one and I really love it. Some people might say it's too racy, I don't care. I feel like Snoop Dogg when I wear mine (and it looks great with this snazzy gold Gucci tie I found on ebay), and always get compliments from the ladies. Also, my personal tastes lean toward 3-button jackets for some reason. I guess I'm just used to seeing 2-button jackets on fat guys, so whenever I try one on it makes me feel middle-aged and overweight (and I am thin). However, if you want a suit you can wear all the time, go black or navy (blah). Or a subtle pinstripe. You can't wear a crazy pinstripe 3-piece to an interview and expect to be taken too seriously. However, if you want to score some action with the ladies, trust me... the 3-piece chalk pinstripe will always do the trick. It has for me.
It just really stands out in a crowd. If you're young, the brand won't matter as much, you can wear just about anything well. I never knew any of those fancy designers, I just picked one up that looked good on me, and I can swear that thing helped me score many times. And when you're 20, I KNOW that's gotta be one of your top concerns (at least if you're like I was at 20).