Hello
For best practice we use anything ending in a '5' e.g. 305, 315, 325 for ceiling moutning as they have downtilit omi antennas. For wall mounting we use an AP ending in a '4' e.g. 304, 314, 324 with external AP-ANT-1w antennas for all round coverage. I wouldn't use a 315 on a wall as thats not what it is designed for.
We do use the 303H as well but only where it is to go over a network gang socket. Also, it only has limited range - a 314 with Ant-1Ws will propogate further.
Hope that helps
Alexander.