I tried a bunch of controllers, and bought the Fatar SL-880 Pro.
It not only had the nicest action, it's also pretty much the least
expensive weighted 88-key controller you can buy, at least in Europe.
Caveats: The user interface is pretty awkward - I wouldn't want
to have to change the keyboard zone splits in a hurry on stage,
for example. It's only got basic controllers beyond the keys:
pitch bend, mod wheel, volume and sustain pedals, and
theres enough structural plastic where you'd want a really good
road case if you were going to gig with it. But I've been extremely
happy with mine. With a good velocity sensitive patch on a physical
modeling soft synth, and latencies set low enough (below 5ms),
I can really "feel" the virtual instrument through the keyboard.
Which, for me, is what it's all about.
That having been said, I really don't rememeber whether
the M-Audio Keystation was among the other controllers I tried.
It could be fabulous too. I've heard in a couple of places that
Fatar OEM's their keyboard actions to Kurtzweil and others.
Who knows, maybe the Keystation has a Fatar action!