I've enjoyed most of those on your list:
-Scar H
-M&P 10
-M1a (socom)
-KelTec RFB
My experience has been:
Scar H -liked it so well I had to have the 16....to sum it up, if I had to get rid of all the guns I have, these would be the absolute LAST 2 that would go.....awesome, awesome rifles
M&P 10-really great rifle...don't "need" it since I have the Scar, and an RFB, but I like it too much to let it go
RFB-bought for hog hunting and getting in and out of vehicle-like fact it's so compact, is easy to shoot, surprised the crap out of me that I've been able to shoot some 1" groups with it using 168 GMM and a 1x6 scope, easy to clean (was PITA to get the gas set right to run with suppressor, but it runs well now-ran fine without suppressor from start)
Socom-really cool rifle, but really heavy and good gawd, it's LOUD....sold it to a buddy whose been really happy with it