Disgby - all around awesome, has new feature incorporates facebook etc and looks really pretty, but ram/resource hog
Pidgin - utilitarian and stilll the best all around AIM Client imo, it came from GAIM, although pidgin still has many minor annoyances and bugs it is overal reliable and doesn't use resources, my favorite part is the plugins, and not as flashy looking and doesn't have nearly as many trendy new features as Digsby
GAIM - outdated and had bugs issues, crashed a lot on XP, but was once the best program around and is the father to pidgin
trillian - generally a giant piece of shit
Miranda - extremely minimal and customizable, takes forever to customize and setup if you don't know what you are doing, still has most potential of any client if you want it to look badass
AIM 6.0 - aims modern reincarnation of AIM 5.0, has new features like video capability, and games etc, is generic aim client works well good for average user, sucks for advanced users because its the official AIM lacks many features that the other clients have
AIM 5.0 w/ deadman middleman - old school minimal official and has all the extra features you will ever need still my all time favorite but very outdated and lacks new abilities
AIM Lite - a stripped version of AIM 6.0 removes all the bullshit not needed in AIM 6.0, good for people wanting quick and easy use of official aim without all the BS