Scope for new AR-15 .....?

I own and regularly use a Ruger 10/22 with a 4x scope. I recently bought an AR-15 with a detachable carry handle/sights with front sight post. I may need to hit slow-moving targets up to 200 yards. What would you recommend? Keep the included A2 sights? Buy a 4-12x scope? Buy reflex-sights? Buy a... show more I own and regularly use a Ruger 10/22 with a 4x scope.

I recently bought an AR-15 with a detachable carry handle/sights with front sight post.

I may need to hit slow-moving targets up to 200 yards.

What would you recommend?

Keep the included A2 sights? Buy a 4-12x scope? Buy reflex-sights? Buy a red-dot?

What are the advantages to each? Approximate reasonable cost.
Update: Thanks to all who provided answers. I borrowed a friend's 3-9x40mm scope; then bought a 3/4" riser. I removed the detachable handle; then replaced with riser and scope. The FIXED front-sight post is NOT visible either at 3x or 9x. I'm keeping the handle (as backup sights) and buying a 3-9x40mm... show more Thanks to all who provided answers.

I borrowed a friend's 3-9x40mm scope; then bought a 3/4" riser. I removed the detachable handle; then replaced with riser and scope. The FIXED front-sight post is NOT visible either at 3x or 9x.

I'm keeping the handle (as backup sights) and buying a 3-9x40mm scope.

Seems to be the cheaper way to go than getting an optics-ready AR then buying MBUS.

Thanks again.
3 answers 3