motoring the wheels

[13or13]

Hi.

Our robot has 6 wheels on it, but we dont know how to motor the wheels.

Should we motor the middle and the back wheels, both attached to the same motor, and the front wheel is connected to the middle wheel.
The other option is to motor only the middle wheel, while the back wheel and the front wheel are free.

For both things we have good and bad thoughts, and we have no idea which one we should choose.