This depends entirely on your needs. If you need a portable desktop replacement, or if you want to play high end games on the go, you need a laptop.
If your main needs are portability, email, web surfing, watching movies, or office applications, a Netbook might fit your needs a lot better.
One final piece of advice: try before you buy. Netbooks and Laptops do not have standard keyboard layouts. They both take shortcuts in different places as far as where to save room on the keyboard. Your typing style might be severely impacted by the way a keyboard is designed on one Netbook or another. Make sure you find one in a store and try it out before you buy. Even if you intend to buy your Netbook or laptop online, make sure you have tried the keyboard in person.