Our opinion is the Push2. It’s built by Ableton for Ableton.
However, since Ableton Live supports almost any MIDI controller on the market, that is more of an opinionated question. That’s like asking what is the best car? It depends.
It really depends on what your use is for it and your workflow. Are you looking for something more for production or for live performance? Also it’s very useful just to have a plain old piano keyboard around too.
Want to know more about controllers? —> See the linked FAQ below