The biggest difference will be in the quality of the barrel.
DPMS offers some upgrades and can be better than what you might consider a 'standard' upper.
There are custom builders that can offer the same upgrades, with the advantage of additional features based on your personal preferences.
You need to determine what your intended use for the upper will be in order to determine what is the best configuration.
For instance, I have 4 ARs for one of three different purposes. Could I get by with one that meets all my requirements?, maybe but where is the fun in that? /ubbthreads/images/graemlins/laugh.gif /ubbthreads/images/graemlins/laugh.gif
Two of them have been custom built for my specific needs (Prairie Dog shooting at longer ranges), one is a DPMS with some specific upgrades for action competition and one is for short range hunting out to 150yds and is extremely light to carry around.
If I were deciding on getting just one, I'd have lots of research done and then have some long conversations with either Mike Milli (DTech on this forum) or Dan Carey (also on this forum) before making a decision and get the best one to meet my specific needs.
The nice thing about ARs is that all you need is one lower with a good trigger and you can obtain and swap additional uppers over time. /ubbthreads/images/graemlins/grinning-smiley-003.gif