If you're buying new don't get an N. I'd recommend the unifi AP lite. It has AC 2x2 mimo. 2x2 mimo isn't very common on devices yet. It's pretty standard in new APs though.
Assuming your device can connect at the rate advertised the below is a general guestimate.
50% direct line of sight < 5ft away with no wireless congestion or other devices using wifi
30% direct line of sight <15ft average with a few devices
5-20% no line of sight, no outside congestion, a few devices
0-1% high congestion, no line of sight.
To get above 50% you have to test like they do in special RF optimized chambers.
wifi also has a lot of overhead compared to wired, they constantly broadcast so new devices can find it.