I have experience with both DD and Del-Ton LPKs, the DD was one of the best and the DTI was very rough, as was a friend's DPMS. I'd pay a little more for DD or go with the PSA Agent recommended. I haven't used a PSA yet but keep hearing good things and the price is incredible. I've also heard they use the same supplier as FN for the trigger group.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek