How is this even a choice?
Ofc it's the Steam Deck.
Linux OS (that you can change to whatever you want, even Windows if in a pinch); built in controller (even if they are only about a 5/10 good if you didn't get the early models with sticky buttons); bluetooth for any other controllers; can actually be used as a dedicated PC when in a pinch (best with a dock since the USB-C port supports PD); can also be used as a tablet through android emulation.
The A9+ has almost no advantages for it beyond it being thinner and lighter (but not really smaller). In fact, because it's an android, it's already gimped to hell because android OS is fucking cancer, unless it's rooted; then there is some potential, but still nowhere near the usability and ability to multitask like the Steam Deck. Even portability is questionable considering its shape, depending on the type of bag you carry/wear.
Idk, maybe I'm just a crotchety old many but I have never liked tablets because I see no real use for them beyond an e-reader. And if I'm going to do e-reading, I'll buy a proper e-ink tablet. Otherwise, I have 0 issues carrying around books (which I prefer anyway due to being more in the moment and feeling the texture of the pages as I go from one page to the next). so maybe I'm not exactly the right person to answer this question anyway hahaha~
