The 802.11g standard is faster. ANY 802.11 b or g equipment will interoperate with your Mac's AirPort card. You want the fastest equipment you can get, so go with the "G" standard. Why? Because anything else you do beyond browsing will be faster. Further, G equipment is newer and is better supported-just try finding up-to-date drivers and firmware for older B equipment and you'll see what I mean.
Good luck and enjoy.