I've never shot a scout. I have a loaded, owned a Poly for a bit, and have shot a socom.
I wouldn't want to be making that decision. Because it's a tough one. When I shot the Socom I was really liking how it balanced and felt and all of that. But yeah the ap is a little bit larger and front post is fatter. So you will lose some accuracy, I would think, from that. For 50 yards and under, it would be superior. IMHO. And faster shooting. Sometimes that small ap on a NM or even standard can light up like a surefire flashlight if the sun is to your back and makes it hard to shoot.
But then you have the drawbacks of a non GI flash hider set up. Or brake, or whatever they call it. You can get a better one from Smith Ent. but I'm not even sure if it's necessary. I've also heard the brake on the Scout is LOUD. But like I said, I've never shot one. I didn't think the socom was loud. But of course louder than a 22" rifle.
Have you got to shoot both or at the very least handle both? It would be a great thing if you could do that. Especially the former. If you know someone.
The 18.5 might give you a bit more velocity, but in all reality I'm not sure if it's enough to matter. I don't think either one is a 1K yard gun.