Quoted:
Go here to compare: http://www.aimpoint.com/products/product-comparison/  (Add the M4s, T1, and PRO from the drop down menu on the right.)

Or, you could also check here where someone has already summed it up for you: http://www.tacticalyellowvisor.net/charts/aimpoint-models  (keep in mind the T1 also comes in 2 moa now.)

ETA: I'd also HIGHLY recommend watching these videos to help make up your mind:  http://www.downrange.tv/show2/

Quoted:
My favorite is the T-1 but even the fiber optics (mepro 21 & Trijicon RMRs) act as big ghost rings for HD...I don't think I'd use a red dot in most HD scenarios...just the flashlight and point shooting.

The AP-PRO has been selling for some smoking deals--like $366/370 over 4th of July, and I can get RMRs cheaper (and I'm a weight snob who prefers light stuff like t1s and RMRs).


ETA-->
I will say the FASTEST reticle for me is the EXPS 2-0/3-0 eotech....even with my minor astigmatism, focusing on the target and having that big circle as the guide to center the aiming point in just works soooo well.  I know they might not be as bullet-proof as aimpoints (since aimpoints are simpler in design),  it's all user preference based on your priorities.  Battery life, reliability (for guys who can't throw out their sight, grab a new one free and put 1000rds on it just to check that it's GTG), reticle, toughness, weight, size, etc.

I know people happy with EVERY main brand; I know people who kick in doors overseas for a living who use the two main brands; and I know for myself and a few others here it's been a LONG search to figure out what we like best....I've owned at least 5 EoTechs, 4-5 aimpoints, 4 RMRs, 3 Acogs, 4 1x-4x scopes (2 MTACS, 1 TR24G, 1 TAC30) and at least a few others (in the last 12 years).  TOMACs probably owned more--he's settled on Mepro21 triangle and 1-4X MTACs (I think); I've settled on an acog with a RMR on it and T-1s.  If I had no astigmatism, I'd probably be back at EXPSs, but (a) I do have astigmatism,, and (b) I'm lazy and like leaving the T-1 on all the time....though if I needed it, I'd probably have to dial it up for a weapons light use/bright, which wouldn't be much faster than turning on the eotech, etc.