So which camera is the one you'll reach for most often, especially when you're in a hurry? Of course, the answer probably changes over time. For me, it was the Olympus E-PM2 for quite a while; lately it's been the Fuji XF1 (probably because it's new). And I suspect it may become the Fuji X10 for a while.
Fuji X20 here. It's the best do it all for my use, great for street, relaxed walk, hiking/climbing and motorbike. Was the X10 before, equally good but with less usable raw.
X100. It helps that it's basically the only camera I have besides film. Comes to work with me in my bag almost every day.
In the five and a half months I spent overseas it was always a case of "what other camera do I want to use (if any) alongside my Olympus E-M5?"
Right now it's my Pentax Q plus f1.9 prime, as it's such a tiny package and I'm having a lot of fun experimenting with the digital/art filters.
Over the years... Contax 139 (film), folding Zeiss Ikonta (6x6 format, 120 roll film), Rollei 35TE (film, long time), Leica Minilux (film), NEX-5N then GXR/M now Sony A7r. I never considered the D800 a grab and go camera. The A7r is both grab and go as well as primary camera, the nirvana I've been looking for since going digital. Hopefully the answer will still be the same this time next year.
I wish my phone were usable but it's crap. June 23rd next year I'll be replacing it, perhaps with photography in mind.
The iPhone 5 camera is surprisingly decent. My biggest complaint is the major distortion at the edges. It really stretches things out, and makes a person have big forehead! For real cameras that I tend to grab as of lately, it's "my wife's" XF1.
