Usually we put howies... very effective, 0 oil cost. Armored Cars work too, but they get more easily killed by tanks, especially HTs, due to their lower range. Walls are also more of an issue with ACs. Under the bottom line imho they are not cost effective...
However, with the buff in Bazookas, I think having RPGs swarm out of the TC also doing splash damage regardless of research (HT!) have potential to obliterate an army, including any HTs, if they get close enough. Additionally, they are hard to kill, as they have high HP and not getting the „tank penalty“ at airstrikes.