SLR Magic 12mm. But if you're doing alot of handheld. best to get anything to stabilize the camera since it's so light.

I have tried using various lenses with my GH2 / Blackbird stabilizer so here's my experience:

Focal-length-wise I'd say anything from 12-25mm is good - you have to avoid extremes. Anything very wide will really show up any movement (you can use 7mm for example but it needs a lot of care) and anything narrow will not really be that much use anyway in a stabilized shot, and it will also show up camera movement too much.

AF is essential because you won't be able to touch the camera / lens when it's on a stabilizer.

Aperture will be an issue unless you can find a wide-aperture, stabilized lens. If you want low-light and stabilized camera, it's probably better to use a lens which is the right focal length and which autofocuses. They are your two priorities. You can't do anything about focus issues in post so you have to get that right - whereas you can work some magic on low-light, noisy images with noise-reduction.

I've used the wide end of the 14-140 with great success (on a stabilizer I find it's better to switch the OIS off - but whatever you do you may also find you need to add further stabilization in post).