If this is your first AR, I'd stick with .223/5.56 which means the MK18. Ammo is considerably cheaper, so you'll shoot more.
I have a DD MK18 upper and I like it so much I bought a second. Light, maneuverable, easy to get on target. Plus, since you're primary purpose is HD/plinking at the range the 10.5" barrel shouldn't be a problem because the distances of any potential engagement are presumably under 50 yards, so the velocity you lose out of such a short barrel will really be a non-issue.
Now if you already had a couple of standard AR's, were looking at a barrel under 10" or wanted to shoot suppressed, my recommendation might change.
And pay zero attention to the poster who put down DD. They make a very high quality, accurate and reliable gun and probably have one of the best rails in the business. Throw on a red dot (look at Holosun, Aimpoint if you can afford it, or Primary Arms if you are on a tight budget), buy a couple of extra mags and as much ammo as you can afford, and you're ready to rock.