i would agree with getting a dual sport to learn to ride on, but you have a higher seat height then other bikes with one, and you will get bored with it quick. i would buy the bike you plan on owning for a while right off the start. you will get the hang of riding real fast, and then you will already have the bike you want, and won't be spending a crap ton more money getting two bikes.The main thing to learn is throttle control and clutch control. once you get that you'll be good to go, and will want a bigger bike.
A great starter bike that I have had experience with is the Yamaha FZ6, it basically has the R6 engine but with more low end torque that makes it more street friendly. It also sits a little more upright which can be a little more comfortable on long trips but it is bad azzzzzz when you open the throttle up and let the RPM's rise. It also carves thru the curves with the best of them, check it out and try to get a test drive and I bet you will be impressed.