PSP, followed by Gameboy Color, followed by Advance SP.
I recently got a Retroid4, and took an amazing trip down memory lane with Mana Khemia, MG:AC!D, FF Tactics Advanced/A2, Monster Hunter Freedom Unite, and a bunch of pkmn ROM hacks. All of them easily held up today.
Unless SteamDeck counts, in which case it wins hands-down.