Here's my KAC arsenal so far. Plan on getting a SR-16 CQB and an LMG (whenever they come out) in the near future, but I'm pretty happy with it so far.
My favorite is my KA SR-16E3.
Upgrades: FULLY upgraded, including m170 spring (this is my DMR), reinforced torque gears, G&P m170 motor, dimpled outer barrel, AWS Stealth mosfet, and pretty much everything else inside upgraded as well.
My CQB gun is the Bravo KAC PDW
Upgrades: high-speed setup w/ Element high speed motor, 13:1 gears, 11.1v lipo, AWS Stealth mosfet (coming soon), etc.
Also picked up a K