I have both the ZN's and the RHA MA750i's and I would think the RHA would be a better gym headphone; they feel slightly lighter and they have integrated ear guides, which I prefer (less fiddling and more stability). Also, the shape of the RHA's allows me to more quickly get a stable fit in my ears than permitted by the ZN's shape. And finally, while both headphones have quality cables, the RHA cable is a little more flexible, a little more supple than the ZN's cable. As far as sound, both the phones have quality, bass-oriented sounds but I think the ZN's tend to be a little more fun sounding. Another consideration - both headphones have large, heavy remotes, which might be a problem depending on the kind of gym activity you pursue.