802.11a (aka WiFi5) - Theoretical speeds up to 54 Mbps (with a fallback to 48Mbps, 36Mbps, 24Mbps 18Mbps, 12Mbps, 9Mbps, 6Mbps) in the 5 GHz band. Not compatible with 802.11b.
802.11b (aka WiFi) - Theoretical speeds up to 11 Mbps (with a fallback to 5.5 Mbps, 2 Mbps and 1 Mbps) in the 2.4 GHz band, the most popular standard. The majority of WiFi HotSpot locations and equipment utilize this.
802.11g - Theoretical speeds up to 54 Mbps (with a fallback to 48 Mbps, 36 Mbps, 24 Mbps, 18 Mbps, 12 Mbps, 11 Mbps, 9 Mbps, 6 Mbps, 5.5 Mbps, 2 Mbps, 1 Mbps) in the 2.4 GHz band, extremely fast AND compatible with 802.11b.