Depends on whether you want a variable power optic or not.
For what you describe, either the Nightforce or the Leupold MK4 1.5-5X...
It just depends how much you want to spend.
The Leup is going to run you around a grand, and the Nightforce is in the $1400 range...
If you're awash with cash...get the best...the Schmidt and Bender Short Dot...
but be ready to part with $2200 or so....
If you want to go with a fixed optic, the Trijicon ACOG is hard to beat.