Both small cameras are selling for about the same (low) price. This is not just a theoretical discussion of specs - we have the videos!
Advantages LX7: compact, fast f1.4 lens at wide end with IS (no Nikon, Panasonic, Canon prime lenses that are both fast (f2 and below and IS and silent)), bigger sensor than ALL consumer camcorders, manual control of video settings, 108060p, external viewfinder available.
Disadvantages: no 24p, no manual audio, no external mic, very limited zoom range, not easy to focus manually.
Advantages of EOS M: fast lenses available (kit is f2.0), almost all Canon lenses available - unlimited lens choices almost, APS-C sensor - big!, manual control of audio and video, external mic port, high bitrate video, 24p available, 72060p available, easy manual focus with focus rings on lenses, Magic Lantern upgrade capability gives it pro video features (focus peaking, zebras, live histogram, choice of kelvin temperatures for WB, RAW, even higher bitrates for AVC).
Disadvantages: no 108060p (108030p), no prime IS-enables fast lens, no viewfinder.
Ok, so how do the videos look in dim light? Grand Central Terminal is a real challenge; it is dim. Both videos shot the same way: with the lens wide open.
Here is the new GCT video using the EOS M and the f2.0 kit lens:
You see: The commuters, Grand Central Market, Grand Central Food Courts, cup cake preparation, window shopping, ticket ordering, the Apple Store, breakdancing
. (No sound, though as I forgot to turn it back on after ML playing).
My favorite clip: the Mac laptop; the money shot: the drinking fountain, which was in an unlit corner (1600ISO!).
And the LX7 GCT video:
You see: An LED light show, Grand Central Market, Grand Central Food Courts, Grand Central toy trains, subway shuffle time-lapse, subway musicians.
My favorite clip: the muffin.