Honestly, its personal preference, there's different forks of each, base Firefox is good, if you want a more private fork try Fennec or Mull. With chromium the only two ive heard good privacy things about is Brave and Cromite (a fork of Bromite, a project that looks like it got discontinued as there hasn't been an update since last December). Honestly try both and see which you prefer.

Sorry, I just assumed you were asking about android specific apps. For Apple, Safari is decently private, Apples strong suit is that everyone knows Apple hate sharing things, so while you can't be sure about how much apple collects, you know they're not giving data to 3rd parties. For computer I'd say base Firefox, (or Librewolf if your okay with the lack of auto updating) or Brave.