Heres the breakdown on both:
Both void the warranty.
Both have excellent features in their own right.
Race Tuner is awesome in that it allows you to change rev limits, map cold idle, and does not ride along with the bike. It requires turning off the bike to make every change, and does not program the bike while it is running.
Powercommander is cool because it allows you to change the fuel and spark while the bike is running on the dyno. This is because it is a second computer. If the tuning center has the Tuning Link software, you are in business. With this software, the computer (Dyno Computer not ECM on bike) basically writes the map.
With both products, if the Dealer/Shop/Tuning Center doesn't have an eddy current brake on the dyno and an emissions analyzer, all they can do is map for 100% roll ons. What good is that if the body of the map (Your idle, cruise, midrange) are off. If they are lean the bike will run hot, ping, sneeze. If they are rich the bike will use fuel, oil (if it's really rich), be sluggish and blubber. If they are mapping by seat of the pants, GOOD LUCK.