I have both; I got the LG when they first came out and the Studio display last year during a good sale on Amazon.
The panels seem the same but everything on the Apple one is better, as you would expect.
But lately my LG is starting to have issues with ghosting and color shifts around the edges. It's still ok to use (I'm typing this on it) but I guess it's nearing the end of it's useful life.
If I didn't already have the LG Ultrafine, I would have bought one of the studio displays.