If you are going to buy the LED program box, then there is no difference between v2.0 and v2.1. Since using the LED box, you can change the firmware (software) in the ESC to any one you like. Whether it is stock racing or mod racing.
However if you NOT buying the LED box, then the factory v2.0 and v2.1 firmware are different.
Since there is no new v2.0 available now, you only choice is v2.1 anyway.
I am using V2.1. On the box it says:
New Improvement:
* Current endurance capability increases [by] 15%
* Perfect filtering effect from smaller size capacitors modue