Which 802.11 standard is better ?

There are 3 802.11 specifications widely used today:

802.11a (up to 54 Mbps, 5 GHz)
802.11b (up to 11 Mbps, 2.4 GHz)
802.11g (up to 54 Mbps, 2.4 GHz)

In addition, there is an emerging 802.11n specification with much faster speeds (up to 540 Mbps, 5 GHz), however the final draft of the 802.11n standard will not be ratified until the end of 2009, and all current "pre-N" devices are proprietary.

Maybe the most widely used standard is 802.11g. All 802.11g devices are backward compatible with 802.11b as well, since they use the same frequency band. However, when you transfer data between 802.11b and 802.11g devices, the connection speed is limited to the 11Mbps maximum of 802.11b.

The benefit of the 2.4 GHz radio frequency band is that it allows for greater range than the 5 GHz band. The drawback is that it is susceptible to interference from other devices, such as 2.4 GHz cordless phones.