There's really good information tacked to the tops of most of the forums around here, this addresses your question quite well: www.ar15.com/forums/topic.html?b=3&f=18&t=211481
Newbs should always check out the "Tacked" topics first......
ps - welcome aboard,
ETA - btw, I'm an Aimpoint guy, the EoTech fellas will be along in abit.
I am an Eotech guy, but the Aimpoint is a nice setup as well.
It is really about your preference unless you will be using it for a specific type of shooting, then read the info at the top of the Optics threads like mentioned before, and go from there.
If you are just deciding based on looks, well, then pick whichever looks more uber-tactical to you...