Depends on you and your riding style. Are you a speeder? Does your wrist have two settings - at rest and wide open? Are you sensible and just want to sit upright and enjoy roads at a government mandated pace?
A Ninja 250 will take you all the way to 110 mph and can wheelie with minimal effort, but unless you're going up then flat, not accidentally. Fuel mileage is about 60mpg beating the crap out of it the while tank.It is not going to outrun much but has no problem keeping up with regular cars.
The 500 is not going to accidentally wheelie on you. She's heavy at just under 500lbs but decently centered. Relatively nimble. Nice torque. Will get you to 95mph and still keep you in the low 50mpg range beating it the whole tank.
The 750 will lift on you accidentally. Same bike as the 500 minus the motor and extra power. I believe the mileage is a tad less per tank on average and will go 105 I think it is.
Don't buy something expecting to put it down. It took me 5 years of riding before I had my first drop. It will happen sooner or later, but don't fret over it. Find what will fit your riding style.