From this thread, all the 11" owners except for one got the LG display. One person went into the stores and checked the four 11" models they had on display and three of them had LG displays. It seems that you're likely to get an LG display with the 11", but you could end up with a Samsung. The 13" seems to be more of a "mixed bag."
I have the LG on my 11", and honestly, using the MacRumors ICC profile I'm finding the screen to be quite pleasurable. I didn't previously own an MBA so I can't comment on the differences since I haven't compared to a Samsung screen, but I'm definitely pleased and don't have any desire or intention of exchanging and taking my chances getting something worse (I have the Samsung SSD right now and my MBA is flawless - don't want to risk getting the Toshiba or one with some other imperfection).