I have PSP9. Have used the series since version 3.14. PSP9 makes a few changes in how it handles everything and it took me a little while to get used to it (Particularly how it handles selections on layers). If you are familiar with PSP then I'd stick with the series, you'll find it immediately familiar and be whipping stuff up in little to no time. I can't say whether you will need v9 or 8. You might want to read about the additional features in v9 and see what kind of work you are aiming to do with it and if what it has to offer is what you are needing.

Only your mind limits yourImagination. Let it free.