In my opinion there are 2 reasons to buy the Ally:

1. You absolutely have to play competitive games that require kernel-level anti-cheat (these won’t work on Linux/Deck).
2. You absolutely have to have the highest graphics possible (resolution/frame rate), battery life be damned.

If you care more about the overall experience, ease of use, battery life, input options, color, sharpness, repairability, customer service, software options, etc. etc., SD is the answer.