Either optic will do you fine.
I happen to prefer the Aimpoint, but not due to acquisition speed or accuracy at range. It's a matter of durability and battery life.
Remember that the mount is half of the sight.
There are a lot of folks that make replacement mounts for them, but the only one that I am willing to recommend is LaRue Tactical. They have optic packages for all of the M2-M3 series with their mounts that are barely above retail for just the optic.
Prices for the optics are not that divergent, especially when battery prices are considered. In fact, the top-end Eotechs (553) run about 600-620. An M3 with LaRue cantilever is 569, and the EoTech mounts suck compared to the LaRue.
If you are trying to go cheap, you can get an M2 with standard LaRue mount for 490, or the 511 for 424. That's only a $66 difference.