Stay on topic....
Which AR is the best and combination/setup??!??! Hmmmmmmm - Well I got Diamond on my Assualts and this is a tough answer. But here we go...
USE G
& TARGET FINDER with every AR!! TRUST ME it helps out A LOT!
I would stay away from the SWAT & SMAR. Those guns suck!!! But if you had to use them, make sure you put on Select fire for SWAT and G

!
I recommend TYPE 25, FAL, Scar H, M8 & AN 94. You can't go wrong with these AR's. The FAL was a BEAST DURING CORE CLAN OPS/Challenges. But if you always play CORE, I highly recommend the M8A1. That gun does work and it has a SMG feel to it, so does the TYPE 25. The M27, is very accurate gun with very little recoil. The SCAR and the AN94 are a powerful guns but I highly recommend the G

for the AN94.
My personal favorite/best AR is the Type 25 with G

& Target Finder. I hope this helps and enjoy using the AR's because they were a pain to go through. CHEERS!!