I could simply tell you simply save money and buy a DI system, but I would just be giving you a fish, a small one that's been laying out in the sun a little too long. You'd be far better served with a few facts and considered opinions to make up your own mind
I picked the original AR piston system in mid-length. Here's what an AR piston looks like
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The AR piston is part of the bolt and rides inside an expansion chamber (cylinder) in the bolt carrier. As you can see, it's even got piston rings. Truth is, it's not a direct impingement system. A DI system uses gas directly on the carrier, with no piston or expansion chamber. Gases come down the gas tube, hit the carrier and sends it off. The Swedish Ljungman is a classic example of a direct impingement system
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Eugene Stoner used a different approach. Instead of just blasting the carrier with gas, he used a piston. He took the piston out of the gas block and placed it inside the carrier, eliminating the op-rod. This reduces the amount of heat the piston is exposed to and gives it more surface to deal with that heat. It also keeps the reciprocating mass inline with the recoil and bore to reduce muzzle disturbance.
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Neither system is cleaner, dirtier, hotter or cooler than the other. The difference is where that heat and dirt is vented. The bolt & carrier of the legacy system doesn't run much hotter than that of the PIGB (piston in gas block). With a PIGB more fouling is seen around under the handguards and the gas block. With the legacy system, more is seen in the receivers. Both run fine. The legacy system has had more years of development to work out the bugs.
All else being equal, recoil energy will be the same. It will feel different because of how it's distributed, but it the amount of recoil the round generates is the same.
Practical accuracy will be comparable with an edge to the legacy system if you're shooting bughole groups. Weight should be within a few ounces of each other. Some PIGB upper are heavier, but you'll note those have a thicker barrel profile.
Where you're choice really lies is cost. If both types cost the same, it's your choice as long as the upper is proven to be reliable. Usually, PIGB uppers cost more and offer no real advantage over a legacy upper.
Fort more information, check out the link to Stoner's original patent found in this thread I wrote at M4Carbine.net
http://www.m4carbine.net/showthread.php?t=99050
Here is the rifle I run for HD. It'a a PSA carbine kit that I assembled. Barrel is stainless steel government profile with a 1:8 twist and 223 Wylde chamber. I chose this kit because it was affordable and the important parts were up to spec. After sending the upper back for problems with the feed ramps, it's run reliably every time. I chose this configuration because it's the shortest I could go without having to pin the muzzle device. I like the fit and feel of the Magpul furniture and the H1 Aimpoint is fast, rugged and reliable with a very long battery life. The Battlecomp compensator helps keep the muzzle flat without being as obnoxious as a brake. I mounted a Surefire 300 for when it's dark. It's small, light and very bright for it's size. Burn time is about 4 hours or so. Mounted at the 12 o'clock position, it's easy to switch on & off and the barrel shadow is out of the way
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I hope I've given you more just a fish, but enough to cast for further knowledge until you know enough to make the decision for yourself