If you are a professional, then most will tell you the full version of Adobe Photoshop is a must.
However, it is not the easiest programme to master, (I have tried). My recommendation would be for Paint Shop Pro, which is more user friendly, will do almost anything you need, and not too difficult to master.
By the way, the latest Adobe Photoshop v7 would set you back almost £600.
I have PS7, PSP8 and PhotoImpact on my machine. I can do wonderful things with PS7 but I must admit I'm still only scratching the surface, PSP8 this was a photo competition award, I find very awkward and more difficult to work my way through, probably if I had started using PSP before PS I would think differently. However for value for money I would certainly go for PhotoImpact, This is one very good, reasonable priced programme.