I don't think you should be surprised by the answers you get on this forum, being that this is fnforum, but here's my 2 cents:
I would discount any AR because the 3rd gen rifles are just better; better engineered, more reliable, and DI sucks.
A piston AR is an AR in most respects, and I've held a bias against them since the early days of widespread carrier tilt problems, cracked lugs, sheared off carrier contact points, etc. From the reading I've been doing they seem to have gotten alot of these issues worked out, but the fact of the matter is that the AR as a baseline system was never designed with a piston in mind, and never will be. I don't think I'll ever be able to get over that, but different strokes and all...
I've got lots of trigger time on the real deal G36. It is a fantastically reliable rifle, and the samples I've fired were neglected by their owners, to say the least. Nevertheless, they seem remarkably well built, and I don't think there is any doubt that HK makes quality parts. On the downside, the G36 suffers from those HK ergos. Everyone in Germany must be 7' tall and have a horse jaw, with fingers about as thin as a No. 2 pencil because that seems to be what the G36's LOP, mechanical offset, and charging handle were designed for. Oh yeah, the selector is a little easier to reach than the blowback legacy rifles, but is that really saying much? But hey, the G36/XM8 is on the cover of Tom Clancy video games, so it is ubercool. Again, reliability is outstanding, but the crap ergos cause the novelty to wear off PDQ.
If I were to buy another EBR that wasn't a SCAR, it would probably be a Sig556xi. Handled them at SHOT and I am very impressed. If properly executed, I can see the xi being a major player in the black rifle market.