A lot of the "bad reputation" DPMS got was the nature of their business in years past. Bushmaster was the Lincoln, DPMS the Ford. When Remington started, they were the Mercury. But suddenly the market gets flooded with new blood and they all thumb their nose at DPMS. Oddly, Delton's earned a better rep because they were too cheap to ignore, and they ran well - never as clean or as reliable as a DPMS on average, but better than "enough" for the guys building them. Those of us who had been around the AR-15 block before the boom were scratching our heads - Deltons get better recommendations than DPMS or Bushmaster? WTH?
So then came the whole Windham split and the Freedom fiasco, coupled with the Bushmaster refocus on the ACR... so Bushmaster made some strategic decisions which weren't popular, kicking themselves down the totem pole in the hearts and minds of would-be buyers even more. But they still make an accurate and reliable rifle with as good or better fit and finish than most in their price class... DPMS still cranks out some of the most accurate-per-dollar AR's on the market.
Can't account for taste, I guess. Honda Civic's were really popular for a while there too, never understood that either.
What you'll find for any of these $400-600 rifles, almost all of them are sourced from the same few producers. They all have their little highs and little lows, but overall, if you could field 10 each of S&W M&P Sport II's, Ruger AR556's, Bushmaster XM-15E2S's, DPMS Sweet 16's/sportical/etc in the same price point, you're going to find very similar performance. Good or bad among the fleet would be no more likely than good or bad among the 10 of each brand... They'll all likely be over gassed, so beat up brass like crazy, but run well, all be accurate enough with good ammo, and all be clean enough to pass casual inspection. None will be diamonds in the rough, but finding a turd in the punchbowl won't be likely either.
Ultimately, you'd do just as well rolling dice as to picking based on brand in that class. If one has a stock set you like better, that's the one to get. Everything else will be effectively equal.