Fan and a fan controller

what should I look at for the best fan on a fan controller. Is it rpms or what?

rpms is just speed, cfm is how much air it pushes (60+ is ok but quiet, 100+ is great cooling, but noisy) dba is noise (40+ is loud, 30- is quiet)

Its really just personal preferance. Some people can deal with have 8 Tornados. For others, thats just too much noise. Thats the nice thing about a fan controller though. You can buy a high cfm (cubic feet per minute of air) with a high db, and then you can take it down to more reasonable levels.