nikon. Any mount would need an adaptor but nikon is easier to adapt than canon because it has a physical pin that controls aperture. I believe the sony/minolta af mount is also similar in that regard.
I'm trying to switch over to pretty much all nikon glass because it is the most future proof due to how easily it can be adapted to most systems. I like m43 but I can definitely see myself using something with a S35 sensor in the next couple years.
honestly, I wouldn't really recommend the 24mm, at least personally anyways. I may have gotten a bad one which is highly possible for a third party such as rokinon but I wasn't truly satisfied with it, I didn't find it to be very sharp as I expected and the images coming from it weren't quite as good as I hoped. I do have the rokinon 35mm and let me tell you that is a nice lens, so I don't have anything against rokinon lol. The benefits of the lens though is that it has a nice long focus that's fairly smooth and an aperture ring on it.
I ended up trading my asst. manager at work for his mamiya 645afd, a deal that I feel benefited me much greater haha. I'm looking to sell the mamiya right away to purchase either a zeiss 15mm, zeiss 21mm, or the nikon 14-24mm.
Hmm. Yeah I've heard mixed reviews on it. I really want it to be a good lens because there just aren't many options for a fast normal prime for a GH2. The native panasonic/leica lenses supposed to be super sharp but they are focus by wire, which is huge deal breaker. Everything else is just really expensive.