del-ton i believe is some kind of offshoot of dpms or has some kind of relationship with DPMS.
i have bought a lot of DPMS parts over the years. pretty much everything except bolts and bolt carrier groups. so far all the DPMS stuff seems to be pretty good. i get a lot of my DPMS stuff from J&E surplus --but back before del-ton was swamped with orders i got stuff from there too. got a 7.62x39 barrel on backorder form del-ton right now--matter of fact.
the reason i don't use DPMS bolts and BC&G's is that i use LMT bolts and bolt carriers. now DPMS bolt and bcg may serve you well.l i can't say as i haven't run one.
now M&A had a spotty reputation for quality on some of the mall-ninja sites. people complain about their small parts/LPK and their uppers.
recently i ordered a bunch of small parts from M&A to finish out a lower i was building. the quality wasn't bad at all. everything fit and worked out well. the price was good, the parts are comparable to some armalite stuff i had--which is pretty darn good. remember i am talking about the small stuff not barrels and bolts--
i have seen a few of their uppers. they looked and functioned OK from what i could tell.
the plastic stuff looked a little on the cheap side but i didn't see anything horrible about them at all either. like canted FSB, upside down gas tube- over tight or over loose barrel nutz ect-- like all those internet stories you hear--
i would pick a DPMS over a M&A most likely. however if i found a good deal on a m&a upper i would likely buy it as most of these things are mostly sourced from the same parts. you can about count on 1-9 inch twist, no chrome lining in the barrel, not likely to have m-4 feed ramps, and lastly 4140 steel for the barrel. nothing wrong--just avg ar in the AR world.
i would say it come down to cost. if you had say one you could inspect before hand--that would be nice. in todays out of stock world--you can't afford to pass a decent deal if it is in stock anymore.
from what i can tell M&A and del-ton are deep backordered on most things.