I started out using Audacity and was very unhappy with the results of the sample rate conversion and dithering. Never tried sox. It was recommended to me by Doug Oade to try Wavelab Essential as a good inexpensive program for basic editing. He recommended it because of its quality sample rate conversion and dithering. I have used it ever since and have been completely satisfied. I payed $99 for my copy from musicians friend, but I think it is out of production now so you may find it even cheaper on e-bay. Money well spent, and the multitrack software I have now automatically referenced the wavelab plugins so I get double use out of it.
Matt