As RT said, it depends on what you want/need the AR for. Is there a quality difference between the two? Yes. The Colt is definitely higher quality. But you may or may not need some of that extra quality. And therefor, may not need/want to pay extra for it.
However; depending on where you are willing to shop, you can sometimes find colt, BCM, DD, LMT, and some others in the "Higher Quality" class, for the same price or less than some not as high in quality. And even if you don't need some of the higher quality, it would be foolish to not buy it if it's the same price. I.e. If a Ford F-150 base pickup is $20,000; but they have a sale for an F-150 fully loaded for the exact same $20,000, it would be foolish not to take the fully loaded. I went to McDonalds the other day and asked for burger, fries, and medium coke. The lady asked if I wanted to get a LARGE soda instead, because ALL DRINKS were $1.00. Obviously I got the larger coke.
Some cynics will say that I'm talking about "FOR A FEW DOLLARS MORE", and that translates into $200-$300 more. No, I'm not. I'm talking about the same EXACT price, or even cheaper than the price of a similar AR of lower quality. In one of the other threads here, I posted a link to a Colt 6520 for $899. MOST TIMES, that's cheaper than the normal price of a Bushmaster or DPMS or Rock River. However; there are many people who don't want to shop around. They won't order online and have it shipped to a local dealer. They are impatient. So instead, they buy the local Bush, DP, CMMG, Olympic, etc... for $850 instead of the Colt for $1000-$1100. That is understandable; however; if you're one of these people, then there's no need to ask advice, because you're just going to buy the cheaper one anyway if you're not patient enough to look for sales and such. Not saying you are, but there are some out there. Deep down inside, they know the colt is better than the Olympic, RR, DPMS, etc... but they're looking for reassurance because they can get the lower quality one locally, today, and they are impatient. Whatever. It's their money.
However; the reverse is also good and should be looked at. For instance; I bought a S&W M&P15OR a couple months ago at christmas. I don't have the requirements that a colt, bcm, dd, etc... offer, and definitely didn't want or need to pay extra for one of those guns. But had the colt I mentioned earlier been on sale for $899, and my M&P15 was at normal price of $949; I would Definitely have ORDERED the Colt. Better quality and a better price. However; my M&P15OR was on sale for $200 off, plus a $100 mail in rebate, so I go my M&P15OR for $649. This was about $300-$400 cheaper than a flat top colt. (I wanted a flat top). So for me, the smartest choice was to get the M&P15. It fit all my needs, it's reliable, and dependable, and it cost $300-$400 less. But I was willing to wait.
So, to answer your question, the Colt is better quality than the DPMS. It's better material in most cases and better quality control. I could list the actual better parts, but they might not mean anything to you. And for MOST AR owners, the better quality isn't all that important. However; if you can get the Colt for the same price or less than the DPMS you're looking at, then it would be foolish not to get the colt. But here's the deal. If you're NOT willing to shop around for sales; or you're NOT willing to order online; or you're impatient and want to buy the AR today; then it really doesn't matter; does it? However; if your DPMS is on sale for say $650-$750, that would be a decent deal. I wouldn't pass that up. Basically; if you're going to get a lower quality rifle, which will still be great for most people who put say 1000-1500 rounds a year through the rifle AT MOST, and will be reliable and dependable, at least buy it because it's a great deal. The MINUTE!!!!! You spend $850 or MORE!!!! on the AR, you are in the SAME EXACT PRICE RANGE as the BCM, Colt, DD, LMT, etc... Then, buying the lower quality makes absolutely no sense. Unless you're just looking for someone to rationalize what you bought.
The ONLY PROBLEM I have with some of the lower quality rifles, is their price. I.e. A Bushmaster costs in the $850-$1050 price range. That is NOT worth that price when a higher quality rifle costs the same. But again, local shops will charge more because they know you don't want to order online. There is absolutely nothing wrong with a DPMS. But it's NOT the same quality as a Colt. Anyone who says they are, doesn't know. But if you can get the DPMS for $200-$300 less than the colt; NOT JUST IN THE LOCAL STORE; then definitely buy it if it's what fits your needs and you like it.
P.S. Being you looked at bud's it shows you're willing to look online. Here's the colt for $899 If you want .308, that's a different world. Not on quality; colt still wins out; but on price.
http://www.birminghampistol.com/product/colt-6520/