Voltage Drop and Cable Size Calculator
The larger the cable size the less voltage drop you will see and the less energy you will waste in the cable.
But there is no way to say what size cable is idea for your vehicle because we don't know the vehicle, the controller or even the batteries!
2/0 should be good for 500+ amps and lead acid golf cart batteries tend to top out at 500 amp peek, but you'd never want to sustain that, of course if your battery pack is split up and you have a few batteries in front and a few in back and a few hidden in some other corner then you could end up with some long wire runs and those you'd want to be larger then what you use for interconnects between batteries, but you also need to look at the total amount of electrical cable that you are using in your battery string.
For most smaller passenger cars I'd say that 1/0 is just fine, you might notice a difference while climbing hills or accelerating.