DelTons are pretty decent lowers:
http://www.ar15.com/lite/topic.html?b=3&f=118&t=401668
The worst made lowers out there will still fire under 1/2"
MOA, its the upper that dictates the groups. For every
manufacture out there you will find someone who had
to file a little here or their to accept parts, just the
nature of producing Milspec parts off a 40yr old design.
If I gave you a BillyBobs cheapo lower and a Lewis Machine
Tool composite lower, a table and a micrometer you would
have a tough time saying what was better less the way one
would look astheticaly.