Comparing wireless a,b,g,N: is there a noticeable difference in the coverage area provided by each of the different standards? Do any of them do a better job penetrating different kinds of walls (namely concrete block)?
Wikipedia has a table of the various protocols and their approximate ranges.
There is very little difference between A, B and G and it is likely that you will find transmitter/receiver quality will play a far bigger role in the range you can actually achieve.
N however, specifically added features that increased the potential range - see this article