This is one of the most popular questions I get. 

Eros(Urethanes) -

A urethanes based paint used by most professionals for painting cars and bikes. It is used by most professionals because of it's supper bright and brilliant color. The drawbacks are that they are way dangerous to breath and caution and safety equipment must be used to mitigate this risk.

Acrylics -

These are water based paints that you you see in all the craft stores and Wal MArt. These colors are safe, cheap, and easy to reduce with water. So what's the drawback? They are bland and not very bright. They don't have nearly the glass like deep colors of professional paints.

Enamels -

I put enamels in a class by itself because you can actually have water based enamels like Auto-Air that cross the boundary of water based and enamel.  These paints are generally safe to use and easy to use but more expensive.