Ok what i suggest is find out the BTU/Hour that you need to cool. For a close enough idea total all the wattage in the room. For example you have 3 servers all with redundant power supplies (2 in each), one monitor,and a switch. The PSUs are all 450w, the monitor is 90w, and the switch is say 15w.
So you'd use the formula BTUs/Hour=max watts/0.65*3.413.
It should come out to an AC unit of at least 14675.9 BTUs. Now I'm not sure as to who's got the best AC units but that in my opinion is just a minor detail but I hear that APC has good in room ones. Otherwise nothing can stop a Train... LOL

Hope that helps.