I only have one scope and one AR. It's a 3-9. I like it and at 3X I can run Steve's course with it. I am getting older so the increased magnification helps. I have a red dot on an AR I sold, so I probably didn't give it much of a chance, but I don't think I care for them too much.
Steve, you have forgotten more about this sort of stuff then I will ever learn, but if I had multiple AR's I would have a 1-4 or 1-6 on my run and gun rig and a high magnification scope on a long distance rifle. I use the 3-9 because I think it allows me to shoot up close and out to a moderately long distance. But in a way for me it's a little like an enduro motorcycle.
I really like the Vortex Razor HD Gen II 1-6x. At 1x it's better than a red dot because the eye box is massive and the entire scope body almost vanishes from sight. It's almost like a magic trick. It's the clearest glass I've ever seen and the dot is bright enough to fry your retina. There's literally nothing about this scope that I don't absolutely love. It's expensive and a little heavy, but it's worth it.
I went the other way... If I had anything other than irons on an AR it was a scope as red dots were unknown. Once EoTechs and Aimpoints became common I migrated to RDS's. When the Vortex PST 1-4x came out, I decided to give magnification another try. Well, I no longer own the 1-4x PST. With my eyes being as old as they are, if I can still manage to see it, I can hit it with a red dot... and hit it quicker than I could with the 1-4x. So the low end of the 1-4x didn't do me any good on a DEFENSIVE carbine.
If I know that I'm going to be shooting +200 yards, I want a scope. But I find that in that scenario that I'm better served with a scope that starts at 4x rather than ends there. My thinking is that if I ever have to take a shot that "counts," I'd be better served with an RDS.
Edit: Which is not to say that I disliked the PST 1-4x; I did like it. It just seemed like the wrong tool for me.
I picked up a FFP 2-10 X 42 Burris . I like it a lot. The glass is great and I can shoot little groups with it at well past 100 yards. I keep it on 2 X when not in use. That way it is always ready for close up work. Then if it is something small out past 100 yards I can quickly crank it up to 10 X.
I went with this 1-4x Primary Arms on this rifle and I have to say for less than $120 bucks this scope is awesome, very clear glass in all the power ranges. I really like the dot style reticle also.
I ran it in the carbine course today and it did very well. I really like that center dot on the reticle makes for a bit faster shots when having it on 1x for closer in shots just basically point an shoot.