I went with a 512 after a while of researching, it was an impulse buy to be frank, but I love it.
the 512 is very similar to another Eotech model
without the night vision capability. (and a little less depth for the water resistance IIRC)
one fellow in the link below said it best:
I also had no need for NV, so I went with the 512. As far as the submersion, if I'm 10 feet under water and still holding onto my rifle, something has gone terribly awry and I don't think an extra 23 feet is going to matter to me. YMMV
the 512 has controls on the rear as apposed to the 552 (side)
if you plan on running a magnifier, a side control system might be best, as illustrated by the link below
http://www.ar15.com/archive/topic.html?b=3&f=18&t=442391
Please do not buy based on looks alone. the aim point is a magnificent sight (own one as well). reticle on the eotech is great for fast target acquisition. some will tell you you need the 50,000 hour battery life on the aimpoint vs the 5000 hrs on the eotech, again YMMV.
hope this helps a little bit!