Would I be better off using a rifle kit to assemble an AR?
If you can get the Sport for $540 OTD or better I'd stick with the Sport. PSA's kits are going to run you $500+. Del-Ton's kits are $475+, but you have to pay another $45 to get them with a hard chromed bbl.
I'd get the Sport, slap a set of $25 M4 heat shielded hand guards on it (or MagPul MOE hand guards), and shoot the crap out of it. If you decide you want another AR after a few thousand rounds down the Sport you'll know what you like about a basic 16" carbine, and what you areas you'd rather change. At that point I'd build the DPMS stripped lower into exactly what you want based on what you find you like.
I've owned the $1000+ rifles like Colt, LMT, and Noveske. I've also owned ARs from DPMS and Olympic. I currently have a Daniel Defense M4V1, and S&W M&P15 Sport. I wish I'd never traded the Colt SP1 I had. The Noveske pistol was a fun project, but one I didn't have time to perfect so it went to a friend. The basic LMT carbine was also a great rifle - it was a properly built no frills, nothing to get emotional about M4 style though. The corners cut in materials & build quality on both the DPMS AR-15 pattern and the Oly were obvious. Caveat, I have a DPMS LR-308, and these SR25 pattern rifles seem to be built by an entirely different & better company.
The DDM4V1 with its cold hammer forged barrel & omega 12 FSP rail system is something special. The M&P15 Sport with its T/C made 1:8 twist 5R rifled medium contour barrel, and user upgraded hand guards (Troy MRF CX free float in my case) is a beast. It's not a DDM4, but at a little over half the price, including upgrades, of the DD it's amazing how close the Sport is in terms of feature, performance, and build quality. I think it's an exceptional value in the AR world.