I believe you will enjoy the GS500 more. The power and speed will be much better than the 250 Ninja. Especially since you are coming off the 250 Rebel.
I could either buy a 07 Ninja 250 with 42 miles on it from a dealer for $3000 or buy a 06 suzuki GS 500f with 2000 miles on it from some guy for $3500 maybe less. I am only 5'2" and just sold my Honda Rebel 250 to buy one of these. Which one should I get?