I've had a couple of motorcycles, but I got rid of my last one at the beginning of the summer because they're not nearly as practical as a bike and because they pollute more than an SUV.
(Source: http://www.latimes.com/news/printedi...,1076364.story)

Bike Pros
-> You can haul more stuff w/ trailer, panniers, etc.
-> You can wear shorts without being a SQUID
-> You can park/go just about anywhere
-> You get exercise
-> It's not as cold
-> You don't have to change the oil or wrench on it as much
-> It's usually less expensive, depending on what kind of bike or scooter you get
-> Even though you don't have to have motorcycle endorsement to ride a 50cc (or smaller) scooter (in the US), you probably should still take a motorcycle training course

Cons (bike, pros for scooter)
-> You can go further on a scooter with much greater ease
-> You won't sweat as much (but you still stink like "road" - it's hard to describe but other bikers probably know what I'm talking about)
-> Scooters are heavier and probably harder to steal

Other than that, a scooter is still cheaper than a car but a bike is still cheaper than a scooter. Both are prone to theft - even though a scooter is heavier you still need some sort of supplementary lock.

Good luck with whatever you choose.