From what I've heard Photoshop is better than Photopaint.  I think it is true as of today.  But we cannot say that is always true.  The two competitive software has its own forte.  Photopaint is easier to learn than Photoshop but if you learn Photoshop by heart you will definitely used to it someday.  If you are certain that you will use this talent as a profession not by hobby only, then go for Photoshop.  Why learned the hard way if you have Photopaint which can simplify your work.  I rated Photoshop as 100% and Photopaint as 95%, now which do you prefer?  It is like choosing between Mac or Windows OS. 
Photoshop is expensive than Photopaint.
If you know Photoshop it is an advantage in learning Illustrator, After Effects, Adobe Premiere and other CS.
Why not learned the two if you can?