While the Soft Case doesn't offer the level of protection that the Hard Case can, it does offer easy portability via its belt loop and the ability to play MP3s and charge it while the PSP is still in the case. This would be impossible with the Hard Case.
If you go with the Soft Case, I would suggest considering some added screen protection. Nyko's Screen Armor offers great screen protection and your PSP can fit in this case with the Screen Armor attached if inserted and removed with care.