Taylor WSO's tutorial
on arfcom is certainly worth a read.
there probably isn't a "better" design between the curved-radius ("DPMS" or AR15-style) and the angled one ("Armalite").
the uppers & lowers can be kludged to work if mixed but you're much
better off sticking w/ one design or the other on a particular rifle.
AFAIK, currently there are probably more AR-308 uppers being made in the Armalite design (Armalite, Noveske) than DPMS.
"banned member" has decided to go DPMS pattern on their new finished and 80% lowers, but if you're going to go scratch-built CNC from billet you don't care about that.
personally, i'd go Armalite pattern, but that is just my bias.