On that list you provided I've got hands on with:

Roland XP-60 (loved the action on that one.., I used to own it)
Roland E-60
Korg PA-50
M-Audio Keystation

I haven't played the S-970 yet, but I'm going to assume it has the same keys as its predecessor.., I've played that one.

I think every board I listed is better than the MZX's keys (yes.., even the M-Audio Keystation).

**Important** If you get your hands on an MZX-500 to test out.., make sure you get to play one that's "broken in". Out of the box, or a unit that hasn't had much play will feel completely different than one that has been played regularly. The action over time will become very clanky, the keys will rattle with light taps, the noisy keys will be very obvious when playing fast runs. I won't even attempt a palm slide for organs or synth bass because I worry about the keys holding up.