I went through this process a couple of years ago.
I was lucky enough one weekend to listen to The Classic Records pressings, some UK Plum/1st Pressings , a RL Led Zep II, and also some of the Road Case 45 RPM set, some on my system, and others at darthlakers place.
If money was no object, I'd go for the Road Case.
There was also something special about the Early UK pressings, but finding them in decent condition is difficult, and I think I preferred the Plum Led Zeppelin II over the RL version.
The Classic Records pressings were very ,very good, and certainly much better than some random Aust pressings I already had, as well was the the more recent remastered/deluxe sets than came out a few years ago. I did prefer the UK 1st presses to the classic records.
I've ended up with Classic Records pressings, as well as a UK Plum Led Zep II, and remain on the lookout for really nice copies of UK pressings of the others.