Pistons were supposed to be the holy grail but the "new" seems to be wearing off the whole piston movement. I would buy a decent DI carbine/rifle from someone like Colt, LMT, Bravo or possibly RRA.

Great input. Thanks all for the validation of some assumptions I had.

For a true AR it's probably best to stick with direct impingement. It's what they were designed for and it works just fine. Piston retrofits have their own set of issues (like carrier tilt), so it's not like they're definitively better.

If you truly want something piston operated, then I would buy something that was designed to be piston operated from the get go. An AK, an FN SCAR, a Bushmaster ACR, ect.

Most of the problems people have with modern DI ARs can be traced back to one of three things: bad operator, bad magazines, bad quality AR. If you buy a good rifle (Colt, BCM, Noveske, LMT, Daniel Defense, ect), run good magazines (like PMAGs), and learn how to run and maintain the firearm properly....your problem level should be at a minimum.

Another thing to keep in mind is that carbine length gas systems are the most violent in operation and therefore put the most stress on components. If you are looking for the best possible reliability in the long term, a rifle length gas system might be the way to go.

Another option that is starting to become more popular is the mid-length gas system. This seems to be the best compromise, as you get a longer gas tube, but still maintain the short maneuverable barrel length of a typical non-NFA carbine (16"). I don't own one yet, but for my next AR I'll definitely be looking at a mid-length setup.

I have been very pleased with several Bushmasters that I have owned but most of the better known makers produce quality rifles. It would be hard to buy a "bad" one. I think the original gas system works fine for 99% of users under 99.9% of conditions most people are likely to encounter and I've never seen any need to consider changing to anything else.

+1 for DI. I have a Bushmaster ORC with about 1,00 rounds and it has never failed. There are things you can add to your AR to make it more reliable. Start with a quality manufacturer like Colt, Bravo Company or Spikes Tactical. Get a mid-length gas system. Add a SpringCo blue buffer spring, a BCM extractor spring with back insert and O-ring. I like the McFarland one piece gas ring. Use Magpul PMags. If you want the max in reliability get the FailZero bolt carrier group with hammer. Some think a heavy buffer adds to reliability, I have a Spikes Tactical ST-T2 in my AR. Furniture and optics of choice, mine is Magpul MOE and Aimpoint H-1 micro.

Since you posted your questions in the "Equipped to Survive" forum and not a firearms specific forum, I assume you're wanting a rifle for surviving during hard times - not competition or target shooting. You might want to consider an AK rather than an AR for pure survival (where you can't clean your gun properly, might drop it in the mud or sand, etc.) I'm not knocking AR's. But if I had to drag one rifle of this type into a completely unknown situation of unknown duration, it would be an AK not an AR.

well some guys will say piston sucks some will say it is the best and land bast Gas guns ( DI ) and on and on
we will go. the truth is they are both great guns. but depending
on your likes and your dislikes of each model what you are going to do with it its up to you.

You must see Nutnfancy's gas vs DI vid. Its all true. youtube nutnfancy's piston VS DI vid

I would go DI. It's a proven system and it's more common so parts are easier to find. I think the AR got a bad reputation in it's early years, but those issues have been fixed. Just make sure you buy a quality brand. There's a lot of junk out there.

Here's a good article on how a DI AR performs when dirty: http://www.bravocompanymfg.com/v/vspfiles/assets/images/filthy14_oct10.pdf

And here's a good chart comparing different brands of ARs: http://spreadsheets.google.com/pub?key=pwswheghNQsEuEhjFwPrgTA&gid=5