Those are just samples of which car they may assign you (and there are others) if you book a full size car, you don't get to choose ahead of time.

At 6 foot 3 I don't think it matters all that much at all, he can probably easily fit into any of them. Some have seats that adjust up and down in addition to front to back, which would be a plus, but it's totally hit and moss what each car has.

You can ask at the counter if you want to swap, or maybe even for an SUV.