If you like playing an anti-infantry role, the most important suit to acquire certifications in is Kinetic Armor. Kinetic Armor provides a resist to anti-personal projectiles, which means it provides better protection against the types of ammo that Infantry will use against you.
You will also want to acquire the Anti-infantry Weapon certification that allows the MAX to equip the anti-infantry weapon on either or both arms. These certifications are the MX1 Heavy Cycler cert for Terran Republic, the Quasar VM1 cert for Vanu Sovereignty, and the NCM1 Scattercannon cert for New Conglomerate. In addition to this cert, I would take the Laser Sight cert and attach it to the rail of the weapon to increase accuracy when firing from the hip.