Which is beter.slim or da origina ones?

Functionality wise, they're exactly the same. So if you want something you can just carry easily in your cargo pocket or bookbag, then the one's the choice for you.

However, I have heard of kids dropping the slim ones easily.

The new slims do have a couple new features. One is the ablity to use component cables to hook up to a hdtv and play and I've also heard of a TV tuner add on coming out (possibly, its out in japan) that only the slim will support.