my favorite optic is the trijicon tr24G then the ta31f-g Acog i run a benchrest scope from nightforce on one of my AR15. the wife likes her aimpoint rds.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...
RDS or magnified?
Fixed or variable?
The question you just asked is tantamount to "What tires should I put on my vehicle?". Not trying to be a smart-aleck or overwhelm you...but narrowing things down a bit will certainly earn you a more useful answer.
fun or range use or want to be all milsped up. many guy use what they would on the hunting rifles others want what got to war or at least what they think does. You can slap a 150 dollar red dot on it and have fun or a 200 dollar 2-8 rifle scope and go hunting or to the range.
If you are looking for a red dot that's a more than decent starter scope I would go Vortex Stykfire. I have one and love it for what I do at the range. You can get one for under 150.
If you want crosshair look into Primary Arms 1-4. You can get this for about the same price.
I got both of these scopes to use for a while in order to find out what I really want/ don't want out of a scope when I finally make an investment on a more expensive optic.
I didn't want to drop 5-600 dollars on a scope until I figure out what I really want out of a scope. I figure if I use them for a year it will be worth the small investment to educate me a little more about scopes on the AR.