The correct choice is 802.11ac because it supports wider channels and more spatial streams compared to the other standards. This allows for higher data rates and more efficient handling of multiple simultaneous connections, making it suitable for high-density environments. 802.11b is an older standard, providing much lower data speeds and only operates at 2.4 GHz, which is more susceptible to interference. 802.11a, while operating at 5 GHz and thus less prone to interference, doesn't offer the high throughput or multi-user efficiency required for modern high-density settings. 802.11g operates at 2.4 GHz and also faces limitations with speed and congestion compared to 802.11ac.