I can't pick one. If I could, I wouldnt have so many. For general stuff, and wandering about, its the X100 (or the XZ-1 or the Ricoh GRDIII) but for "special" stuff, like when I want to go all arty and get good bokeh, its the K-5 with one or more primes.
For its versatility it's the EM5, especially in combination with the PanaLeica 25mm.
But, the most beautiful camera to hold was the X100.
Even though I eventually sold it on I still dearly miss how that camera felt in my hands, the way every button and dial clicked and the gorgeous silence of that shutter. Having been spoilt by the EVF of the EM5 I sold the X100...for a start I felt I NEEDED a decent EVF as my plan B whilst learning to shoot via the OVF. That issue has since been addressed and I now wait impatiently for my X100S to arrive.
I get the feeling that if I had an out-and-out favourite camera, I wouldn't have so many cameras...
Based on capability it should easily be my E-M5, but sometimes it seems almost too efficient and is not my favourite camera to look at or hold. Then there is the G1X with its pixel-level perfection, but it isn't the complete package like the E-M5 and is also a bit homely looking from certain angles. My Samsung NX200 has the most wonderful quality materials, controls and display, and finally there is the GH1 which feels more comfortable in the hand than all the others.