Definitly go for DBP. DBP is more powerful and constantly being updated.
If you buy the classic version, you'll also miss out on user made .dll's which are user made expansions. By the time you upgrade the expansion pack so you can use .dll's and other features in the enhanced pack(memblocks), you'll have spent more money than what you would've for just buying DBP.
Just search the Dark Basic Pro section of the board for the terrain pack. See the beautiful terrains? Well, you can't have those in classic, only in Pro.
Your best bet is to buy DBP.
A book? I hate book. Book is stupid.
(Formerly known as Yellow)