First of all sign up for the MSF Course & in taking that you will know a bit more about m/cs & riding. You might even have your mind changed in what you can possible handle for a FIRST bike. So think of the two 500s & remember at first you are going to be making a lot of mistakes, possibly into the wrong gears, possibly lugging the engine like accidently in 2nd or 3rd gear when trying to take off from a STOP sign, problem in tight turns, shock of what 40mph is like when on a bike, to actually dropping the bike at next to nil speeds at the start. So the less plastic on it & the with more pull from lower revs is by far the best. Just remember either of those 500cc bike will be faster off the line when the green light comes on then most cages & the bike can take you up to 90 or 100mph & where can you cruise at that speed & be legal or not asking for speeding tickets or possibly an error in judgment & coming to a terrible crash with the driver of the cage being in the wrong!!!!!!!!
Like any sport be it hockey, baseball, football you have to start from the bottom & work your way up. Reason the bikes at the MSF course will be dinged in 125 to 250cc bikes. Also you are just learning the very thin basics & then you must practice a lot so doing the practice & learning on a peaky engine bike with dramatic stopping power beyond 20% you might neeed, is really sensless.