Dern near Anything.
My best 1000 yard scores were fired using a Super Match M1A using iron sights.
My my 300 WM 1000 yard gun (any rifle any sights) I use a Weaver T-10. Its been working for me for over 30 years.
I don't like higher power scopes because they then to magnify the mirage, washing out the target.
The type scope would be determined by what are you going to do, want a range finder, get a Mil Dot scope. Normal Target shooting for known distance you can get by with any quality scope w/knobs allowing for easy adjustments.