I'd go with the zmax, but that would because they offer a mini or telescoping models. Plus, I think it looks sexy in gun metal. My second APV is almost identical to the zmax, but it is thinner and lighter, totally wicked Vape-Pro.
The only reasons I wouldn't get a vamo is the size, and I've heard that the threads are kind of cheap, but that is just recalling threads..so I'd advise research on that topic if someone doesn't clear that up for you... Zmax, SID, MVP 2.0, itaste 3.0, itaste SVD, Vape-pro, lavatube, vamo..and many others. I know the Vape-Pro and Zmax offer a RMS function, but like I mentioned, that isn't necessary for vaping..e-liquid.