Budget is also critical. And the type of photography?
I have an Olympus OM-D because I wanted lightning quick AF in a smaller setup than my DSLR as I have two little kids and wanted it for days out/family shots etc.
If I didn't need the AF speed to be near instant then I would have very probably gone for a Fuji X-E1 or X-Pro1 for the image quality in low light, the solid build and amazing prime lenses. And I think I've become a Fuji fanboy
But those cameras are on the top end of the CSC price range.
Sony seem pretty good but I don't like the lens choice (without adaptors and messing around) and I prefer the retro style of Fuji and Olympus.
Panasonic are good but I do love the fact that all Olympus CSC bodies have image stabilisation built in so any lens will have IS and they share the same lenses, which there is a large range of and great quality options.
What quality do you need? You can get very good photos from the Fuji X20 all in one camera and it has a viewfinder, fast lens and sex appeal

it's a great little go everywhere camera and could save you lots of cash of you are happy with the image quality from it. I love mine.
Hope that helps.