It's been a while since I took it out of the hangar, but I used a Keelback with a fighter bay and an F63 Condor. I may be wrong, but I feel that the fixed multicannon Condor does slightly more damage to structures than the others. I did, however, only use the Keelback for the missions to destroy generators, might need to go back and fit some SRVs for that.
More recenty, I've been using a Dropship with a couple of dumbfire missiles in the bottom medium hardpoints, turreted multicannons in the side mediums and a gimballed large multicannon. I think staggering fire with the two dumbfires might have a better chance of getting through the anti-missile defences (from what I remember, isn't it basically a load of missiles fired at your missiles?) but I could be wrong again. Also I think the turreted multicannons are kinda pointless since they don't really seem to shoot anything when I assault bases despite my hopes that they'd just blaze away at skimmers, turrets and anything else that threatened me or a mate driving an SRV below me.