ProTools or Soundforge (my choice). Protools interface takes some getting used to, SF is a model of simplicity but with many powerful features under the skin. Like most software at this level, it can load ANY DirectX-compatible plugins too (like the original Radium Fraunhofer mp3 codec, one I couldn't be without. Google 'radium mp3' to find it).
Set your sample rate as high as you can, and don't downsample until all your edits have been done. If you're going to store the files on your PC as MP3 make sure to select 256 as the bit-rate (or higher if your PC/software can do it).
There's a good page here
which lists various wares and their performance.