You can use the 557 with night vision and I believe it can go 30 ft underwater. If you don't need that go with the 512. Both are red dots.
And the underwater part is critical since most of us swim with our AR's.
Great option if your a soldier.
Depends on what you plan on doing with it. If it's a 16" and you don't plan on shooting out past 300yrds then either the aimpoint or the Eotech are good choices. Unless Eotech has cleaned up the reticle many people claim there fuzzy, my 552 is but it doesn't bother me to much. With the eotech you will have a wider field of view at 100 yrds. If you plan on using it for home defense then either red dot will work great. Really comes down to personal preference.
For my 18" game guns I use a Burris XTR 1-4 and a Meopta K dot 1-4 which allows me to adjust the power and reach out reasonably to 400-500 yrds at 4x power and then back to 1x power for close up work and anything in between.
It really does come down to the rifle (Length of barrel primirly), I would not expect to be doing precision long range work with a 16" and a red dot where as you can with 18's and up and a variable powered scope. And again personal preference. The variable power scopes I mentioned and the red dots all run pretty close to the same price so again it comes down to personal preference.
I forgot to mention you can also purchase a magnifier for the red dots which will allow to reach out farther, but it's like looking through a straw.
I would also take a look at the burris red dots a lot cheaper with excellent build quality and reliability.
Hope this helps.