I want to put an Aimpoint on my RRA M4 carbine but I don't know which one. What are the differences? What do you guys suggest and why?

i've got 2 ML3's and love them, one in 4moa on my 9mm AR and one in 2moa on my 5.56 rifle, they're great optics and i'm sure you wont be dissapointed, as for which one to get? depends on what you want the ML2's are good if you dont mind the 4moa dot and less bat. life, the ML3's bat life is around 50k hrs and you can get it in 2moa, i like the idea of having a completly waterproof optic that i know can take a beating that i'll probably never have to change the battery on

idk anything about the M4 i cant imagine it really worth the $700+ vs the ML3's

the difference between the M2/M3 and ML2/ML3 is the M series is NV compatible, if you dont have NV or dont plan on using it with your aimpont get the ML, it's cheaper

I prefer the ML3 (2moa) in a Larue cantilever mount.  The 2moa works well for longer distances and you can crank it up for CQB.  I'd do the M3 if you have a specific need for NV.  YMMV