I have my router protocols set to auto.
If all your 2.4 GHz devices are capable of N, then you should disable G. Otherwise, the headers will be sent as G, with the data sent at N. However, this is a minor slowdown, compared to the hit B causes. Many years ago, I had a notebook computer that came with B only. I then replaced the WiFi card (losing the dial up modem in the process) to get G. Shortly after, the Mississauga library stopped allowing B.
I haven't lost my mind. It's around here...somewhere...