Kato is of course the best designed and smoothest running mechanism and to my non-expert eyes, I like the Kato's shell. The GG-1-specific pantographs are visually very well done, but are non functional (non-sprung or equalized).
Bachmann chose a very unusual design for the mechanism, specifically the trucks and their sideframes (design I have never seen before), but it is a good runner. The shell details seem ok too. Its GG-1 specific pantographs are not quite as good looking, but still not bad. The best thing about those pantographs is that they are sprung and equalized, so they will actually follow the catenary wire.
As for Arnold model, I would not even put it in the same category as the other two models. It is just an old N scale model that back in its day was the only choice available. I also believe that the old Arnold model's chassis is unique to the GG-1, and not simple a GG-1 shell placed on a chassis made for some European e-lok.
Isn't BLI also coming out with a GG-1?