Buying new rims...17's or 18's?

I just upgraded from 16-17 inch rims. My car does feel somewhat slower but I think it is because the rear tire is taller and it took some gearing out of the car. 18s look awesome though. I would have gotten them if tires didn't cost so darn much.
 
ok if you use a tire that make it to the same height as it would be from the factory then how would it slow you down? Anyways 18s slow you down from a take off but at high speeds the 18's have an advatage over ther 17's nobody tells you about that one now do they
 
17's for me, but i'm cheap...... I'll take a 17x9 wheel w a 275/40 thats what i'm going to get very soon..... Now the hard part is finding the right style of wheel, Which you already have...so what i just said is kinda unessesary....