802.11g WiFi Shield

The speed of 802.11g/n is not much important here. since Arduino can not fill in 11 Mbit/s of 802.11 b. but since 802.11n support 5.0 Ghz and it is much less crowded than 2.4 Ghz. The WiFi Shield which support 802.11n 5.0 Ghz is the way to go.