Depends, if you’re going to just use it for steam games/emulation (though it does support other launchers)? Steam deck all the way, and you’ll be amazing support as well.

Anything that requires Windows? (Quite a few multiplayer games with specific anti-cheats come to mind) then I’d go with the Ally, though I do have some gripes that would keep me from it, like battery life. Though it does, from what I understand, handle windows way better than dual booting the deck