I can't remember exactly what the rarities are for prizes, but people have received anything from a codestone to a high-level paint brush like pirate or maraquan. It's so random and so varied that it really is a bit of a gamble. I was lucky enough to get a pink pb on the Neopia Central 1 map I converted.
Remember that once you convert a map, you can never earn pieces for that map again. So if you're looking to make np and don't mind working extra hard, you can collect all the pieces to a map multiple times and sell them, before finally converting your own map.
As for the level 2 prizes, I've never heard from anyone who's converted one but the prizes are supposed to be better. *shrug*