I have a daniel defense AR15 on the way. I really think they offer you the best value for the money. That's what I would go with.
IMHO, Colt's overpriced for what they offer.
I would skip the DPMS. While the price point is attractive, they skip over things like M4 Feedramps, chrome-lining the bore (for bore hardness and increased barrel life, plus increased slickness for easier case extraction), properly staking the gas key (improperly staked gas keys can come loose, resulting in the bolt carrier not getting enough gas and failing to cycle properly), M4feedramps (lowered feedramps to help feeding, especially 75grain or even 44gr varmint hollowpoints--this is more needed in a carbine length rifle with shorter dwell time and harsher cycling).
Here's the all famous "chart" as a handy reference for what the 'mil-spec' parts do and why they're included as features.
M4 CHART
I think Rob_S does a better job of explaining the features than I ever will.
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THAT SAID: I had a Rock River Arms AR ('RRA') which did not have all the 'features' of the chart, and it ran like a spanked monkey. Similarly, I've personally observed Plan 9's RRA which has also been tremendously reliable through thousands of rounds.
I'd spend the extra $200 to get the DD, then spend the extra $350 you saved on a familiarization course.
Hope this helped.
*ETA* Re: 55 gr. Theoretically, 1/9 is a better twist for 55gr, but, I have not seen a noticeable difference shooting 55gr out of my 1/9 or my 1/7 twist barrels. Just the other day I shot 3 touching shots at 50 yards, using 55gr PMC, 1/7 twist barrel and iron sights. Me Personally, I would go for a 1/7 twist as it allows me to shoot things like 75gr Hornady TAP, which is considered an optimum home defense cartridge.