I did both, and I think motorcycle tours and bicycle tours are very different.
On a bicycle, you'll be a lot closer to nature. A lot of paths I use are closed to motor traffic and you can't ride with a motorcycle.
On the motorcycle, you can cover more ground and see a lot more different places in the same time. Also, cars don't feel as dangerous, so you can ride roads with lots of car traffic that I wouldn't ride on a bicycle.