If you're gonna take it easy and your just wanting experience then I'd start out with something like a used Honda Shadow VLX (600cc) or a Yamaha V-star (650). Both can be had used for bargain basement prices and neither one will be overwhelming. Hands down they make great beginner bikes that you won't mind keeping around for a while. (60+ MPG doesn't hurt either)
Most importantly, for someone of your size, you'll appreciate the extra power of a 600 over the smaller 250's. Trust me, you WANT something that can get you out of the way in a hurry incase you need it to.
That said, the mechanics of these cruiser-style bikes, such as the center of gravity, trail geometry, upright riding position, and overall handling (by that I mean smooth, not twichy) is much better for a beginner who is still developing their riding technique.
Sport bikes can be a handful if you're not careful and I don't recommend them for any beginner. (Just like your high school didn't furnish you a Corvette or a Mustang GT for drivers ed did they?)
At the very least, before you buy, take a beginner MSF course and see if riding is for you. They'll teach you the mechanics of riding in a safe and controlled environment and they'll even provide the bike (no risk of wrecking your own).
It's just my opinion. Take it or leave it.
JR..