Allow me to be one of those three people then....
I've tried Reaper and Bitwig so far, and Bitwig is hands-down better in terms of use with the Keylab. Bitwig "understands" the keylab and verything pretty much works without needing you to co figure it. Bitwig even supports categorized preset browsing (a-la AnalogLab) - and I'm shocked that Bitwig and Arturia aren't trumpeting this fact to the market.
Reaper, despite being my preferred DAW, is shocking. I've wasted weeks trying to get it to play nicely with the Keylab, with poor results. The folksover on the cockos forum blame Arturia for not integrating with Reaper, but I've gone through the Reaper SDK and none of the features that Arturia would have needed are present (or, at least, visible and documented).
Your mileage may vary. Keyboard mag seem to think that Ableton trumps Bitwig, though I've yet to see any suggestion of integration between keylab and ableton. Logic apparently works well to.
If you're using windows, start off trying bitwig!