Bicycle
Pro:
Lower cost of operation
Ease of parking
more exercise
sometimes I just feel like riding my bicycle

Motorcycle
Pro:
Faster for trips of more than one mile (it takes time to put on the safety gear that I would not use on a bicycle)
less likely to get a traffic ticket (bicycles are watched very closely where I am)
travel on my schedule rather than the transit services
more comfortable in cold weather gear
sometimes I just feel like riding my motorcycle