There seems to be a great deal of variation between individual panels, so blanket statements about LG vs. Samsung don't seem all that helpful.
My personal experience:
rMBP #1:
Bought a 2.7/16/768 in-store on the day the prices dropped. October production date, 8 MB cache on the CPU. It had a Samsung display, which had a somewhat darkish area near the middle of the screen. Whites seemed a bit yellow, especially with the brightness down. Color saturation was great.
I brought it back two days later. The tech couldn't see the dark area, but agreed to swap it for another unit.
rMBP #2:
This one had a November production date, 8 MB cache, and an LG display. No IR/ghosting, but the colors didn't seem quite as vibrant, and whites had a pinkish cast. If not for the pink, I think I would have stuck with this one and hoped for no IR troubles down the road. (I'm still a bit skeptical that the LG panels are categorically doomed to fail.) But I pressed on, and went back again three days later.
While waiting for my appointment, I put mine next to one of the demo units, which turned out to have a Samsung screen. The range of color on the LG was better -- the grass in the zebra photo had a more natural shade of green, whereas it had a "neon" look on the Samsung. Some colors seemed more saturated on the LG, which I did not expect. Brightness and whiteness seemed more similar than I expected as well.
This time I got a different tech, who was reluctant to swap, since he couldn't see anything noticeably wrong with the screen, and I had returned one already. After some polite and patient discussion of the 14-day return period, the need for an accurate display, etc., eventually he put it next to one of the demo units to compare. It was a different one than I had been looking at, but I think also a Samsung. Mine looked noticeably pink and dim in comparison, so he agreed to do the swap.
rMBP #3:
Somehow with upgrade price changes, I ended up with a 2.8/16/768. Production date unknown -- the serial number websites don't recognize it yet -- but since it's a 2.8, it must be an early 2013 model. It has a Samsung display. The black level doesn't seem as deep as the LG, and I still remember the first one as being more colorful, but otherwise it's just about perfect. This one's a keeper.
Moral of the story:
- While there may be trends and recurring themes, each individual display is different.
- No display is "perfect", and can't be expected to be. Apple is bound by the limits of physics and the realities of manufacturing like everyone else. That said, at these prices, it should be "awesome".
- The polite-but-firm approach is often successful. If you can get someone on your side, they are more likely to help you.
I hope this is helpful to someone. Good luck to all affected by this issue.