Stag makes one hell of an entry level AR, with a life time warranty to boot so you won't be disappointed. I beat the crap out of mine and it kept on ticking. Running it about 1000 rounds before a cleaning... and I ran her very dry. I would shoot it, let others shoot it, its been banged off barricades, dropped, rattled around in the trunk. Shot it until the barrel was smoking out of the hand-guards. Seeing as I have a ton of spare AR parts laying around that the gun smiths from work "donate" to me being me
I tried my hardest to trash my Stag. She kept going.
I have since sold off and built other AR's but if your looking for a solid AR and a good price, by a nice company, they are tough to beat specially for the money.
Personally right now my "GO TO" AR-15 is a BCM 14.5 middy upper matted to a stock Stag Arms lower. The way I figure it... if STAG (read CMT) is good enough for Noveske to contract for their receivers... it is good enough for what I do.
CMT ( Continental Machine) is Stag's parent company, and they have been making AR-15 (and M16) parts for quite some time.. for many AR makers. They also make some Aerospace and automotive parts as well.
As far as DI vs gas piston... the major advantage I would guess is to people running a suppressor. Other than that... even if they might be a tiny bit better in some way (personally I don't see it) it does not justify the cost difference in the price tags. Reading a interview with Noveske, he stated that they have no interest (at the time, i forget how long ago it was) in gas pistons because he felt they didn't perform any better.