Saiyan, definetly. Why? Well, because:
1. The tail is really useful and you can train it to not be your vulnurabillity (like Nappas and Vegetas);
2. You will never get old. You will die, eventually, but even at the age of 100 you'll look and feel like 40-years old guy;
3. Everything related to martial arts you can learn in a week, while human has to learn it for a few years;
4. Your power is limitless: the more you fight, the stronger you get;
5. Even though you are not born with an abillity to fly or shoot beams, it is easy for you to learn.
Probably something else, but I don't remember right now.