I personally worry about avoiding flats more than anything. I like the Continental Gatorskins for that.

Currently I'm still using the tires that came the bike that I bought in September 2010. They're Bontrager Race Lites and I've been very happy with them.

Once I wear out the tires I currently have, which are 700x23, I plan to switch to 700x25, since everything I read about tires indicates that wider tires are more comfortable and also a bit faster. If 700x28 fits on your bike, it would be even better.