I’m converting all the time, but never MP3 to WAV. MP3 is lossy compression, so you are drastically increasing file size with no improvement in quality. If it’s just a case that you have to send files somewhere as WAV, then you have to do it. Best would be to go to the original file and convert to WAV. If the option exists to use MP3s, go for best quality settings. Your won’t lose much as MP3s are good enough for CD quality IMO, unless you are purist, and want to record the Vienna Philharmonic. I use Amadeus. It’s cheap, easy to use and converts to many file formats.