The G1 doesn't support video at all so it's probably not a good start
The obvious choice for video is the GH1 as the GHx cameras offer improved video over the rest of the range. The GH1 + 14-140mm can be had for under £700 now which is around the same price of the lens alone, the 14-140mm lens is optimised for video which means a continuous aperture iris and silent, quick AF.
In terms of whether it's good or not for video that's a difficult question. For me I like the GH1 as a video camera because I'm mainly a stills person and therefore for video I prefer having a device that handles like a camera that I can use with my existing lenses. The GH1 also has the advantage of a comparatively massive sensor which gives you access to shallow depth of field (with suitable lenses, the apertures aren't really wide enough on the 14-140mm) and very strong low light performance.
However from a pure video point of view there does seem to be quite a few complaints with the GH1. Many are due to the choice of codec and its settings which to be entirely honest I don't particularly understand, the hacked GH1's seem to get around a lot of this but Panasonic locked the cameras down and it's harder to get this type. There also seem to be complaints about the auto-gain control on the audio which can't be modified and there's no 'power zooms' available, all zooming is a manual ring type which can be difficult to achieve smoothly.
As is probably clear I'm not that familiar with the video side, I'm happy with the GH1 as a stills person with video on the side but it may be different from a purely video approach.
John