I've had the vortex sparc on my rifle for a year now, and can't be happier. Got it new at academy for $200. Right when you take it out of the box, it just feels solid. Great sight t great price.
Ive used Eotechs, Aimpoints and irons. Looked through but not shot with ACOGs.
I liked all of them, and they served their purpose well. For short range work its hard to beat an Aimpoint H1/T1.
Light and tough as nails, but maybe not as forgiving as the Eotech in terms of field of view. The ACOGS had great glass, but the eye relief was an issue for me. I really wanted something as tough as an ACOG, with a more forgiving eye relief, better field of view, and could switch between 1x and 4x without having to change my sight plane. Ended up with an Elcan Specter DR 1-4 and have been exceptionally pleased with its performance. Of course the buis that come with it are hideous, so i keep a set of Troy flip ups as well.
I have to agree with UMB. I prefer Aimpoint's for RDS. I don't like the fixed power part of ACOG's. I've tried a few variable scopes like the SS 1-6x and the Burris 1-4x. Both were nice scopes and I'm considering going back to a variable. However, I had a chance to check out UMB's Elcan and if I had the kind of $$ he has, I would definitely be picking up one of those. It is the best optic option I have seen for an AR. If you ever want to unload it UMB, keep me in mind.
UMB, in your experience is the 'wandering zero' / POI shift a problem that you read about on the Elcan fixed or is that one of those internet rumors that gets repeatedly propagated?