Four MLas for damage (group 1) and a MPLas with two MGs (group 2) for crit-seeking and cool-firing. Originally, I had an AMS in there but decided to mount a BAP instead because the single AMS's protection is insufficient if you are operating away from the group and tends to give your position away. The BAP helps you spotting, gather target information for your MGs and lets you light up ECM-guys as long as you stay close. The target-info-gathering module is pretty much mandatory for this build and radar deprivation in combiantion with your mobility helps to solve most LRM problems. I know the XL280 goes faster for the same weight but the XL275 is more versatile as it can be used in some ravens, centurions and hunchbacks where the XL280 wouldn't fit... and I don't have one.