Depends what you'll be using it for.
If you dont need much space then go for the very small capacity SSD's. If you want a normal amount of space then go for the regular large capacity hard drives.
I couldn't live with a 40GB SSD drive, not enough space for me. So i'm going for the Samsung NC10 with the 160GB HD.
I'm just guessing having an SSD will be much cooler on your lap, no more burned thighs, besides it's easy to add a memory stick for extra space.
The Samsung NC10 is a great price though.