To upload to digital streaming services (or other distribution methods online) the file type needed depends on the method you choose to upload your music. Tunecore requires Uncompressed .WAV files. From Tunecore's website:
"In order to upload your music properly to TuneCore, all audio files must be 16 bit (sample size), 44.1 kHz (sample rate), 1411 kbps (bit rate) stereo WAV files."
Soundcloud will allow you to upload .MP3's or Uncompressed / HD WAVs, but Uncompressed or HD .WAVs will sound even better on Soundcloud than .MP3's will.
Distrokid will accept .MP3, .AIFF or .WAV files. From their website: "Audio files should be WAV, MP3, AIFF, CDDA, MP4 (m4a), Windows Media (WMA), or FLAC. If you're sending a WAV, we accept up to 24-bit, 96 kHz, or less. 16-bit, 44.1 kHz WAV is typical but pretty much anything works."
CD Baby accepts .MP3 and .WAV files, but recommends .WAV options. From their website: "Uploading MP3s is kind of like taking a picture of a picture with a digital camera and emailing it to us. Then when we encode it to send it to partners, it's like we print out the picture of a picture, take a picture of it with a digital camera, and email it to them. It makes much more sense if you send us the original picture, i.e. FLAC or WAV files."