My first bike was a Honda Hawk NT650. It was perfect to learn on. However, they are kind of rare, so I suggest the modern day equivalent ... Suzuki SV650. It is a 'twin' meaning it has a different feel than a 4-cyl CBRF2 for example.
My second bike was a VFR750 which was a sweet bike, but too much for a new rider.
I own no motorcycle right now, but if I were to buy one, I would find a used SV650. Something cool about the torque and feel of a twin.