Most AC MLLs are better then domestic UCs. You could argue the newer UCs look as nice/a little nicer than the MLLs I've been to in Canada (YYZ, YVR transborder, etc.), but AC almost always has better food, all booze is free, etc. I really dislike that they seem to have gotten rid of Frutopia, but even off-peak hours they usually have a decent selection - soup, salad bar, chips/salsa/pita chips/humus, etc. I also like their cookies better.
Just one opinion...I haven't been to the old (or new) MLL in LAX, though. As a *G lounge, it should be open to any UA gold/plat/1K on any itinerary.