How to Combining/Merge files?

I have three .wav files that I want to combine into ONE .mp3 file

Question: Is it better to combine the three .wav files into One
.wav file, and then convert into .mp3? Or combine into .mp3 first
And then combine? Or, is either way OK? I want the BEST sound I can get.

Dell Vestro 400, Intel Core 2, 2GB, SD RAM, Windows XP
Audacity 2.0.0

Once you make an MP3, that’s the end of the production, so yes, you would be doing all your work in WAV and make an MP3 as the last step.