Was facing the exact same question some months ago. After a dozen or so cheap midi controllers I became so fed up with all the crap out there, that I simply bought the most expensive one out there: the KVC 1, and it's the best thing I've ever bought.

Didn't get the chance to try out the SL88 (grand). Liked the idea of having a few additional buttons on there. But then when will you ever use a pitch bend on the piano? I've got different midi controllers for those synth/bass/anything-non-piano patches. Plus I simply use an ipad as logic controller, and wireless keyboard/mouse combo for more complex stuff.

Anyway, the Kawai's keybed is simply incredible. Couldn't believe how much difference a keybed makes in playing virtual pianos. Bet you wouldn't regret getting it.