I use Mainstage with my Worship team. We use it to play our loops AND it is my live synth rig. I really like how I can load up a set and easily flow between songs. I also like how when I select a new song it also sets my soft synth for that particular song so that all I have to do is play my midi controller to trigger my sounds/patches. Again, it makes it easy to flow between songs. I can hold a pad... switch songs .. and then the new pad will sound and the old one will release when I play the first note. Mean while by hitting "play" the click and loops begin in playback. For rehearsal it's nice because I use markers making it easy to jump to different positions.
I consider myself a Mainstage expert but lately have been eye balling Ableton. I have the demo installed and have 15 days left. So far I can't get it to do everything I listed above that I do in mainstage. I can get it to fire loops, okay that part is easy BUT when I go to a "Scene" (hope my lingo is correct) it would be nice to have it ALSO have the correct softsynth and patch waiting. Is this possible with Ableton? I've looked for the usual YouTube tutorials and have not found one. Surely others are doing something similar to what I'm doing .. or maybe they stick with Mainstage for this sort of setup. Any help, suggestions, even links to YouTube tutorials would be appreciated. :)