For the vehicle coverage: VAG505 and MD702 both can test your car.
But MD702 covers more than just VAG cars ,but almost all EU cars
For the functions: VAG505 reads and clears the codes of all system. MD702 can not only read and clear codes, but also read the live data.
For the special functions: both can do Oilreset and EPB.
Prices: I am sure MD702 is mor expensive than VAG505.
So, pls based on your situation and make a wise decision.
BTW, MD702 update interval is shorter than VAG505.