Like Collin alraedy said, it depends on what kind of application you are running. Also the more users its better having a better CPU and ram which the AP 115 has more than an AP 105 for example.
If i were to put APs in a auditorium which i know that every AP could have a bunch of devices connected to it(not really that i need a lot of BW as ill be just giving internet access) but i would need that it support a lot of users per AP then i would go with AP 115 or AP 135... and if the budget can, an AP 225
Between the AP 115 vs AP 135 i guess it could be better the AP 135 as it has better CPU, than the AP 115. I mean let say im getting like 75 Devices connected to my AP or 100?
I can tell you that for example i got this client in which he didnt want to buy a AP 135 becuase of this price, he bough AP 105 even if he adviced them that they should buy the AP 135 for their auditorium.
Even with that we lend them an AP 135 a while after he bough his AP 105s, and he said there was a big differente in performance that he could feel it, so he bough APs 135 for that audotorium and moved the AP 105s to a lower density areas.
Cheers
Carlos