The iPhone, if recent, is way more powerful than any of those other options. On Switch, the viewing distance is very short and it’s slow to generate chunks.
I have played it on the Sony Vita, Nintendo Switch, new 3DS/2DS XL, and Retroid Pocket 4. The retroid I still have not figured out how to map the controls well and it is a bit glitchy (using the android app version of Minecraft). So based on my experience…if you care about the latest OS and Minecraft version…the switch. If you don’t care about the OS or Minecraft version, the Vita was a great experience.
It is worth noting though the Switch version has troubles playing multiplayer with non-Switch consoles and the Vita and 3DS versions aren't up to date and I don't think they have infinite worlds.
Definitely one of the newer Retroid devices. I have been playing on my RG405M but unfortunately the screen ratio and size makes it a bit of a challenge with some of the UI overlapping itself.
A Bluetooth controller or one of those telescoping ones though would probably be even better than that especially if you have a decent phone. I don't really use this method because the Bluetooth method feels a bit awkward and the telescoping controller involves removing my case which is annoying and it prevents me from using my phone while I play.