The 17lber and 37mm both require direct hits on running troops to kill them. Aiming at the ground will be ineffective unless you happen to hit them directly.
The 88mm (if set to AA shells) does have a burst radius and will kill multiple troops in one shot. I have done that many times.
I believe HE tank shells will also kill multiple troops with one round (blast radius), but I would have to verify that, as it has been a while.
I tend to use the MGs on troops when in a vehicle.
<S>
KP