To be honest, frankly neither! iOS games used to be a big deal to me, back when Modern Combat was essentially Call of Duty for mobile (without microtransactions) and NOVA. I loved those games, especially the online multiplayer aspect. Over time though, games of that caliber stopped being developed or went to a microtransaction style pay-to-win game. the only games I play on iOS now are things that don't require a lot of input like True Skate or Tiny Tower. Mobile games just feel too shallow for my tastes I guess!
Gaming on a Mac has also gone down a lot for me since I'm holding out on installing Windows 10 to play old titles on Steam like Half Life 2, so my macOS game options are Civ 5 and Lego Star Wars TCS.
I save my gaming for my Xbox mostly since I can play the style of games I enjoy more there (Prey, The Elder Scrolls, Fallout). But, if I had to vote between gaming on macOS and iOS, I'd go with iOS since there is quite a bit more developer support there.