AT mines, both for offense and defense. I save mine for deployed Sundies normally, however I'm not against picking off a stray MBT or Lightning if my squad is pinned down.
1st : AT mines to setup defense around base 2nd Betties inside the base 3rd Ammo pack since i spent all my resource pts in 2 secs
If no one in my outfit is on when I log I'll run over to Peris Amp to repair Gens and turrets. Typically I'll find there is an Inf in the base and we'll make the rounds while he overloads Gens and I stabilize or repair them. If the guy gets uppity and decides he wants a kill he catches an AP for his troubles. lol
Almost always AT mines - I have no other AV as an Engineer, so having the ability to demo vehicles when I can is invaluable. I'll swap to AP when doing base assaults or defence so I can mine generator doors and SCU's. I never carry or cert the starter ammo box though. 5+B box is already L3 and can't be taken out of my inventory, so why bother?
If you REALLY want to ruin someone's day, you can always place AT+AP inside a room so that when one triggers, the both detonate. Ideally, place a sneaky couple of C4 on the odd surface on the edge of the blast near the door - to kill their buds letting them go first to check the way for mines themselves. Only downside is how vulnerable to random screw up this setup is, so it is rarely an opportunity for deployment outside of 'mine the spawn before the base is capped to get revenge on those campers'. If it works though...
Also you can drop pod on top of them with sneaky spawn beacon placement. You can even Hot Drop on the very same base you are fighting at. - TR Field Engineering Corps is ever vigilant of new ways to help our siblings in arms fight off the scum that threaten our homes.
Yep it's good fun. I also repair turrets often because the majority follow the zerg straight after the gens and SCU has been repaired.
Last night I joined a public squad for lack of anything else to do. I got bumped into Delta and noticed it was mostly Engies. As we were capping bases the Platoon Leader was giving squad assignments out and Delta's was pretty much stay and repair the entire base. We had LAs a medic, and an Inf in the squad that all stayed with the Engies to get the base up and kinda defend it from the immediate expected back cap. Worked out pretty well. Granted bases were still getting back capped behind us but PlatLead would pull us up to the next base in time to get the cap points and we'd rinse/repeat.