Range - The Tesla is lighter because of composites, the batteries are substantially larger, the batteries Tesla uses hold more charge.
Speed - The Tesla is lighter because of composites, the motor is tweaked for speed, the 2-speed transmission is how they got to the speed they advertised.
Looks - The Tesla is built by Lotus in England. Look up the Lotus Elise and tell us what you thinkit looks like. GM is building their own car.
The down side to the Tesla is that the batteries, which do hold more charge, are only rated at 500 hrs. GM's batteries are 20 times that life. The Tesla's batteries are welded individually, 6000+ places to have a short.
Because the batteries have a higher internal resistance the regenerative braking on the Tesla has to be set lower than the Volt, working the already tired Tesla batteries harder than the Volts.
2 passenger Tesla, 4 passenger Volt.