Be sure it's carbide tipped. 6" or 8" should be fine in your saw. 6" is generally easier to spin, but 8" offers deeper cut and higher tip speed. There are some great 8" sets that don't offer a 6" version. The worthwhile sets tend to start @ ~ $85, and go up from there. You're likely to waste your money if you spend much less.
The best bang for the buck that I know of is the Delta/DeWalt 7670 set....Craftsman offers a version of the same set for $100. Freud, new Irwin "Marples", CMT, and Oshlun sets are all worthy at near $100 too, but IME the 7670 sets cuts better....it also has a great carrying case. The best set I've used to date is the Infinity Dadonator....that'll put you closer to $200.
I'd avoid the Avanti set at HD, Mibro, HF, Vermont American, the older Irwin, the Oldham sets, or other off names.