Just built my AR with a Del-Ton kit on top of a Stag stripped lower.
I loved it because I bought all the "aftermarket" parts (DPMS barrel, YHM handguards, YHM flash hider, Tango Down pistol grip, ARMS BUIS, etc.) already installed and ready to go. In the long run, I ended up saving a few bucks, as well.
I don't know the quality difference betwen LPK's, but mine installed just fine.
Quality was great, customer service top-notch, and fast shipping. Received it within a week of ordering it. Plus, they test out the upper before shipping out.
Next time, I'll probably build the upper myself, but for my first kit (since I'm a newbie) it was a great choice.