Which file type to export for recording a lecture?

I record lectures, but don't really know which file type to export is best. I want file size to be small, I don't care too much about the quality as long as it's not terrible (terrible being the 32kbps type of quality). It's just listening to someone talk for the hour, no music or anything. So like what file type/ recording options should I use? I'm using Audacity to record...using the schools computers...meaning I only only options of output are MP3, AIFF, WAV, GSM, Ogg, FLAC, and MP2 files.