Wi-Fi standards sound more like a bingo game than a comprehensive list of networking options, 802.11g, 802.11n, 2.4 GHz, 5 GHz, legacy 802.11 b/a standards, there are plenty of choices and not a very consistent way to tell which choice is the best.
Generally, 802.11n is better than 802.11g. It offers much faster data transfer, though fewer devices support it than the g standard. As more devices use 802.11n, the g standard will eventually go the way of 820.11b and become an old, legacy protocol. 802.11g functions only on the 2.4 GHz band, while 802.11n can be deployed on either the 2.4 GHz or the 5 GHz range, and that is the newest big question in Wi-Fi setup.
The 5 GHz band, on the other hand, is broader and much less crowded. Before 802.11n at 5 GHz, 802.11a was the only Wi-Fi standard to use the 5 GHz band, and that standard quickly disappeared in the crack between 802.11b and 802.11g. Some cordless phones use the 5 GHz band, but these are fairly rare.
when it can use multiple/wider channels. An 802.11n router can increase performance by taking up a 40 MHz chunk of the band instead of the standard 20 MHz chunk, delivering data at rate above 100Mbits/sec. Since the 2.4 GHz band is narrower and more crowded than the 5 GHz band, the latter is a much better choice for ensuring the top speed in your wireless network. Of course, this requires devices that support 5 GHz 802.11n networking, a much less common feature than 2.4 GHz devices.
To determine which band is best for your wireless network, you need to ask yourself what your devices can use. If you have several wireless devices that already use 2.4 GHz and you can't easily replace them, hold back and stick to the band most traveled. If you're starting with a clean network slate, go for 5 GHz and watch your transfer speeds peak in the much more spacious airwaves. Regardless, a dual-band router is your best bet for legacy support and room to grow.