It really doesn’t matter. If all your computer have 802.11 G cards then set it to G, if some of your computers have G cards but others have B only cards then set it to B, because it will allow for all of the G and B clients to connect to the access point. If you have absolutely no idea what kind of cards all of your computers have, then just set it to B, because it will permit great web surfing with minimal client hassle. The only point you will see lag is when transferring big file across the internal network.