AP11 comes with mounting for ceiling rails or wall mounting. High placement on a wall or ceiling will give you better coverage for a space compared to having it low.
AP11D comes with a desktop stand or wall mount. Given it has connection ports -- an uplink plus 3 output ports --, you likely want it down low and accessible. Some get installed "in wall" where there is a Ethernet wall outlet. Down low, you won't get as good coverage for the same space but the difference should be slight.
If you are trying to decide between them, I'd answer first whether you need to output ports. If not, I'd go with the AP11. If yes go with the AP11D and put it where you can access the ports.