Read:
http://www.tirerack.com/tires/tirete....jsp?techid=51
I suggest replacing the rear tires only with a comparable performance tire (i.e. if the rears are ultra high performance, stay with ultra high...........if the rears are maximum performance, stay with maximum performance). If the tread on the fronts dictate replacement also, then look at replacing all four with a tire performance spec of your choice for your needs.
If replacing all four tires - If you are just tooling around, I'd suggest a nice high or ultra high performance tire, a maximum performance is not called for. I like Michelin, Bridgestone, Toyo, Yokohama, Pirelli, BF Goodrich. Less performance, but tire life should increase and noise should decrease.
I'd go with the alignment check that Hot Foot suggests also.