I have both and I prefer the steam deck. The Ally runs games better when they run, but the trip there always sucks, to the point that you never want to pick it up.
The Ally is actually much more of a “linux-like” experience because you can get more out of it, but you have to put a lot more work into it to get there. The steam deck is like a console.
I just bought one of these. It hasn’t even arrived yet. Guessing there’s going to be a return soon.