i'm not really a fan. its personal preference more than anything else. it will slow you down and hurt your gas mileage, but probably not enough to really hurt you.
Worry about looks first, and then secondly either performance OR ride comfort (upto you what order).
Going from 14s to 17s on my Integra (I know, 14s, right?) the smaller tires at 205/35 made most driving in the city really uncomfortable. If your butt (and passengers) can take a harsher ride for style, do it. I'm not saying don't, I'm saying know what you're getting into, no one told me!!!
I have 19's an love em. Cant compare to stock because these were what was on the car when I bought them. Only thing with mine is that the edges of all 4 tires are cupping and have to be rotate and in perfect alignment or they will eat away the edges. 15k miles on my new tires and there is still a lot of tread. Tires can be found cheap. I paid 600 at discount tire for the set. Local tire shops around here wanted 230 per tire.