To be honest, its not really the program that makes the most difference. Its the quality of the plugins that youre using. I mainly use Wavelab, as i find the wya you use the plugins in real time is a lot easier. The wave's plugins are rated as the best, so get hold of them. Its also got a lot to do with knowing exactly what you are doing. Mastering, unlike making a track, are completely different. When making a track, you can just fiddle with summit till you get it to sound right, but as ive found with mastering, you have to know what you are doing, and understand the reasons why.

There have been some really usefull posts on mastering on here, so just have a look through mate.