PC: Game was designed to be played on PC so the controls/mechanics work great, first to update, free modding add tons of new content, customization, and re-playability. Works with console controllers too. My recommendation.

Switch: Portable and I'm told the controls are nice. Actually updates pretty quickly for a console version. No mods. If you fall in love with Stardew and want to play it on the go, or already play games a lot while you travel, this is also a solid choice.

Xbox/PS: Functionally similar to the Switch but slower to update since their indie workshops just don't seem to care. Not portable, no mods, no reason to get either version over PC or Switch.

iPhone: Literally the worst version of the game money can buy. Very slow to update, mobile controls are jank, has bugs the other versions don't, and no mods.
Android: Similar to iPhone but gets updated first and can run mods.