Well…
I’d have to say I think the absolute best support vehicle I’ve found is actually a tank

Can I do that?
In H2H.fr (IIRC) the OT-85 can carry 12 (loaded with a Soviet Guard squad), has the 85mm for killing all but the heavy MBTs from the front, MG, (in campaigns even a 12.7mm eventually!) and a flame-thrower

. Alternately, load them with “Tandostanki) (sp?), recon, and AT team. I like to add a recon team when I can to drop reverse-slope and spot for the infantry/AT team/tank.
When playing GE, I’ve found a 251-variant that mounts dual (quad?) MMGs, similar to the Quad .50 HTs that the US and SO have. This however can carry 4. A GE Recon Patrol riding one of these is the bane of enemy scout infantry/snipers. The Recon Patrols spots them, and the HT rolls up and mows them down. They make good forward mobile AA assets. I also like throwing 50mm mortars on Beobs. They’re short-range fast support wherever the FO goes.
Ok, ok. Not true Infantry Support vehicles. I know. SturmTiger/Brumbar bring the heat, but I’ll have to agree that I’m partial to the STuG 42s.