Horse charge I'd use a large ram/butt/bash, with their OB, perhaps modified by the driver, definitely with charge attack mods.
Hit by the body or wheel, same, incidental attack (+/-0 OB) but with charging bonus could be quite a bonus. . .(if you charge up 150' on final approach round it's +150 OB)
Run over by the horses (likely result of the ram attack) large trample/stomp, incidental attack, massive DB penalties to a downed foe, and still charge bonuses would apply IMO. Double attack for a 4 horse chariot (run over by one, then the other).
Run over by the wheels, incidental attack again. Large Fall/Crush (perhaps huge for the larger carts) being run over by a wagon/cart/chariot wheel is far worse than a wider soft tire, and that's bad enough.
Scythes, even small ones, would be nasty. . .non spinners (blades on the body anywhere) I'd use a scimitar attack, perhaps falchion for a heavier blade. For spinners, even short 6" hub blades, I'd use Broadsword due to the solidity of momentum behind them. For the big ones on large chariots I'd use the 2HD sword table.
All of this assumes someone can't bail out of the way for whatever reason, but getting hit/run down would massively suck.
The purpose of the hub blades was a specific terror, the fear of dodging but staying in melee range to attack the driver/archers. . .to avoid hub blades you jumped back twice, so in avoiding attack you make it neigh impossible to strike back. Vs PCs, in my experience, they can be nasty, since PCs often insist on attacking back, even if doing so gets you dead. . .the need to be able to dodge but also strike at range made the 2 weapons that killed off chariots the thrown spear and axe. . .usually used on the horses, but sometimes the occupants. . . .though a block of pikes like a greek phalanx would be a poor target too, since again the horses would bite it. . .you could hassle them with drive by attacks until someone did a sprint up and horse stab or threw something.