I actually just got the large "UL" version in today. I had been using the medium original version. The difference in the two pillows is that the "UL" model uses a lighter weight material, as well as only uses 1 valve, rather than 2. My medium, original pillow weighs 3 oz (without the stuff sack). My new, large "UL" version weighs 2 oz (without the stuff sack). Also, the large "UL" pillow will also pack up smaller than the medium original pillow, although, both are quite small when packed up.
However, the material on the original probably does feel just a little better next to skin, although, I don't think that the material on the "UL" is uncomfortable, but I haven't actually slept on it yet, only laid on the floor with my face against it. But I use then inside a pillow case too, so the feel of the material is not important to me, but the weight is.
IMO, if you don't have either and just want to buy one, I would suggest the "UL" version...