If there wasn’t a weird monster, backpack, or out of place alarm clock in the middle right one, that would’ve been my favorite. The alarm clock isn’t even within reach of a bed to snooze it or turn it off. The backpack makes it too cluttered. The view through the window and the colors are my favorite, however.
As-is, the bottom two are the ones I like most. I love the color of the bottom left and I like the nature of the bottom right though I am not a fan of so much orange.
Top left looks best as a default wallpaper in my opinion. Nice mix of colours, not too bright or too dark, and generally seems appealing while not being too distracting.