Panasonic GH2 vs G3 vs Sony Nex 5/7? Must buy and enjoy camera!

Contrary to what Feijai says, the m4/3 cameras can use the same number of "other" lenses as the NEX cameras. The adapters are widely available. Many people use Leica M lenses on both systems. On the other hand, the NEX cameras have focus peaking, which makes them easier to use with manual focus lenses. Quite a few people on this forum will tell you, however, that the Panasonic lenses work best on m4/3 -- better even than Leica lenses (for a variety of reasons.)

At the margins (high ISO, very large prints) most APS-C cameras, will have slightly better performance than the m4/3 cameras. Of course, you're back to carrying around full-sized lenses, just as you are with any APS-C system. I've never quite understood the utility of having a very small body with large lenses -- If I'm going to have to carry around a large-lens system, I'd go with a Nikon D7000, which can use the full Nikon system, plus all of its heritage lenses, terrific flash system, etc., plus, you get a much better viewfinder...for a penalty of 1 pound per body. If I have to carry thirty pounds of photo gear, 1 pound extra won't make any differences, not for the advantages it brings.

I currently carry a full two-body, seven lens m4/3 system, including a 100-300 IS lens (equiv 200-600) in a briefcase. That's the difference.

The NEX system should show the advantages of APS-C over m4/3, but doesn't, because the lenses are not very good. They are okay for kits, but when you're talking about marginal utility -- like really big prints, rather than just big prints -- the poor lenses are more important than the slight difference you get in sensor quality, IMHO. And there are more speciality lenses for the m4/3, including a 3D, a superb wide zoom, a fisheye, a very good 45mm macro, an excellent 45mm portrait, and finally, an f0.95 Nocton in native m4/3 mount.

Also, of course, the GH2 is probably the best movie camera out there right now...