You're probably going to get mixed opinions here but, in my opinion, an external USB 2.0 would be better than an internal. With an external USB drive you can move it from your desktop to your laptop as long as you have a free USB port. The only downfall with external drives is that they are more expensive, otherwise, you can purchase an external drive that has the same characteristics as an internal...such as size, RPM, cache, seek time, etc.
-Mike