Honestly? There is not a tiny bit of difference between them, and anyone who says that there is, is lying.
I used to use PRO, not the "legal" way though (this stays between us, yes), and the only difference is that you get a PRO skin. That's it.

After i got a new Lappy, i just started using BASIC again (i lost the installer for PRO, and good ridens). It wasn't worth downloading from Pirate Bay.