You should never buy larger condoms than you need just to impress other people. If the condom is too loose, there's a really good chance that it will slip off inside of your partner, leaving you susceptible to more STDs and unwanted pregnancy in some cases.

On the flip side, it's also not good to wear a condom that is really tight. Not only is it not good for the blood flow in the area (if it's cutting off circulation, it can do some real damage if left on for more than 15-20 minutes), but it can raise the chances of breakage quite a bit.

A condom should be snug enough to where you can't pull it off in one fluid motion while erect, but at the same time it shouldn't be squeezing you to a level of discomfort. Width is a bit more important than lenght as well. most condoms are pretty long, so as long as your girth fits comfortably in there, you sholuldn't have to worry about too much (unless somehow the uncovered base of your penis is being entered inside of someone, and in that case I say ouch for them).