Here my answer is going to be a little different. The Panasonic GH4 is arguably the best of the bunch. Beyond having manual controls while shooting video, it has a host of other features and abilities that make it the best suited mirrorless camera for video work, in my opinion. The GH4 has 4K video if you need it, but it also has compression choices that have more minimal impact on final pixels. On top of that, the GH4 is one of the few still cameras that has an "all pixels" video mode. This special feature grabs 1920x1080 pixels without sub-sampling directly from the center of the frame (which means it's a crop of the entire sensor) and produces some of the best quality telephoto video work I've seen out of anything short of very expensive pro gear. Just beware of using that feature at high ISO values.
The Nikon 1 and Sony E/FE-mount cameras are no slouches for video, either. The Nikon 1 models have quite good color, better than many dedicated video cameras, plus they have manual video control (despite being mostly automatic cameras otherwise). The Sony A5000 and A6000 models have very good low-light capability for video work, and the Sony A7s has incredible low-light capability for video work. Coupled with the 16mm f/2.8 (E-mount) you can stick the small E-mount cameras into very small spaces where you wouldn't ordinarily be able to do video from.
Most of the rest of the cameras I write about on this site do adequate video for most purposes, but none really stand out as do the ones I just wrote about.
Finally, be aware there’s a dedicated video mirrorless camera: the Blackmagic Design Pocket Cinema Camera.