Lumpy is right...the debate betwee the 2 rages. The bottom line is you can't go wrong with either. Everyone has their personal preference; if you can, find someone who has one or both, and see which one you prefer. There are military/LE versions of both, and "civilian" versions...the civilian versions are less expensive.
I think the Eotech/Holosight reticle takes a little getting used to, but once you do, it really becomes second nature to you. I don't have an Aimpoint yet...hopefully within a couple of weeks. I got a Bushnell Holosight instead of the Eotech for budget reasons, but I'm very happy with it. Depending on prices in your area, the Bushnell can be $70 to $100 cheaper than the Eotech. Both come with a mount; just slap it on the rifle and tighten the hex nut.
Also, if you're buying the military grade of the Aimpoint, you're paying about $35 to $50 more than the Comp C, and you'll need to get a mount of some variety...which adds another $85 to $100 to the equation for the mount, depending on what you get. The Comp C comes with a 30mm ring to mount out of the box.
If money is no object, then just get the one that suits you the best. You're gonna hear a lot of sh** from folks who have a preference...it should be fun [:D].