WAV is the best option in my opinion because it's lossless (uncompressed) and I care more about quality rather than file size, but if you want to cut back on file size I suppose MP3 would work. But really, if it's a short sound, just go with WAV. Those settings you had should work, as long as it's actually mono and not just joint-stereo or something weird like that. Also, MP3 sounds can't loop, as far as I know.