My HHKB with hasu's BT module. Because One With Cup Rubber.
But that's cheating!
Or I'd say my M with a BT adapter.
I'm talking about native BT keyboards. Matias One and the Filco one count as they have native BT, but I'm more interested if someone has found a decent one in the plethora of cheap scissor switch ones out there.
I was going to try the Microsoft Universal they are getting rid of at Best Buy, but they didn't have one on display. The sale guy said it felt like the full size version of it, but I have my doubts. I tried the Microsoft 'folding' one on display and I didn't like it--not enough travel.
I had a cheapee Amazon basics keyboard that I gave to my father-in-law in India after my HP touchpad started having the ?-battery issue. It was pretty decent (but probably not as nice as the MS Universal) and I wish I would have kept it because I really need it now--lesson learned--don't give away stuff you might need even if you don't need it right now.