As you know Ableton Live on Mac supports both the AU and VST3 formats. But keeping in mind that:
For Windows users VST is cross platform. Provided the other Ableton Live user is using the same version of the plug-in, so they'll be able to open the set and the plug-ins will be available,
AU plug-ins may have different preset handling than the VST3, or vice versa,
AU plug-ins do not support a direct MIDI out. If you wish to route MIDI from a plug-in you need to use the VST3 version instead,
Please don't use the AU and VST3 versions of the same plug-in in a Live set.
Turn the plug-in folder off
Open Live's Preferences to Plug-ins and check under "Plug-In Sources",
