There used to be a comparison spreadsheet floating around on the Net. Somehow, it disappeared. They have some good comparisons on Youtube.

I'm gonna put my money on Colt, since Bud's has LE discounts on Colt. I'm in the process of brooming those two M&P 15s. I'll make some pocket change, but not much. Looks like I'll be going with a 6720 to start, and a 6940 later for distance. The 6940 is looking good, but it's .8 lb heavier than the 6720. Both come with BUIS. 6940 has a free-float barrel, plus other nice features.