TL;DR

When installing plugins for LogicPro X, only Audio Unit (AU) is needed.

Breakdown

Slate’s installer actually has awesome descriptions of various formats!

slate_plugin_formats_description

  • AAX Pro Tools plugin format, Pro Tools 10 (32 bit) and later (64 bit)
    • RTAS is for older Pro Tools
  • AudioUnit is Apple’s plugin format, used in Logic, Studio One, Ableton Live and many more.
    • This is what Audio Hijack uses as well.
  • VST [aka VST2] is Steinberg’s plugin format, used in Cubase, Studio One, Ableton Live, Reaper and many more.
    • The original GOAT. Can be 32 or 64 bit, depending on the plugin.
  • VST3 is Steinberg’s new plugin format, used in Cubase, Studio One and Wavelab.
    • Supported in Ableton Live 10 onwards.