You can use GarageBand if you'd like, but you won't be able to add arrangement markers for Live Tracks to reference. Ableton Live can be used for composition, but historically MainStage doesn't sync as reliably to files bounced out of non-Apple DAWs, even if the file format is still .aif or .caf.
What Gear do I need?
Troubleshooting Sunday Guitar
My instrument/controller isn't connecting
My Song-Specific Patch is Different from the Demo
Customizing Your Song-Specific Patch
Sunday Keys Version 2
Using the Tonic Pad Player
Getting Started with Sunday Keys for MainStage
Troubleshooting Sunday Keys for Ableton
Getting started with Sunday Keys for Ableton