I get this question a lot...
"What version of Ableton should I Buy?"
Some basic differences:
INTRO: 8 Scenes, 4 Audio Outputs, 16 Audio / MIDI Tracks
STANDARD: More Sounds, Unlimited Scenes, Basically Unlimited Outputs and Tracks
SUITE: Tons of Sounds / Instruments, Unlimited Scenes, Basically Unlimited Outputs and Tracks
If you are going to be running tracks, and don't need more than 8 scenes or 16 tracks (most people), then INTRO is great. You can always upgrade later if you need more.
If you are going to be running a lot of tracks and audio outputs, get STANDARD
If you are going to be recording, creating your own tracks, get SUITE
For a full comparison, check out the chart here: