Ehm... I don't think that any other application will be as good as Photoshop, it's really a HUGE and complex application. Yeah, Paint.net is good for photo retouch etc. but Photoshop got so many professional tools etc. I'm on Photoshop
While Paint.Net is a good tool, Photoshop has more features. Also I prefer the interface of Photoshop to Paint.Net, probably because I have used Photoshop for a long time before I tried Paint.Net.