G is, first of all, faster than B, coming in at a theoretical throughput of 54mb/sec versus 11 for B(note, both of these numbers are pretty optimistic indeed; but G is still well faster). Also, G gear, especially the newer stuff, is much more likely to support superior security technologies, WPA and so on, while most B stuff only supports WEP(yeah, yeah, there are probably exceptions; but generally speaking your average G setup is more likely to support WPA and the like than your average B setup).
Both B and G are in the 2.4 gigahertz band, and G is backwards compatible, so there is really no advantage in terms of interference and the like, one over the other. Which one you want pretty much depends on how future proof you feel like being, and what sort of uses you are putting your wireless to. G is obviously newer and, unless N gear(or A gear; but that is pretty unlikely) takes over in the near future, will be around longer. If you are just using wireless to browse the internet B will be fine. The nicest fiber-to-home stuff you can get(at least in the US, some countries are rather lucker in terms of connections) is only about 15 mb/sec and pretty much every broadband connection is rather slower than that. If you are going to be transferrring things over lan, you might want G gear. Transfers over B aren't terrrible by any means, only around as bad as USB1.1; but if you are tossing around DVD rips you'll appreciate the extra speed.