For my money the 150D is a smidge better than the 150LS on optical quality and is a half stop faster to boot.
Our test of the Schneider 28LS
and Phase One 28D
showed them to be difficult to distinguish between.
So it's not purely a matter of one line is "better" than the other.
But the 55/110/150/240 LS lenses are all really great lenses. The 110LS and 240LS especially which I'd put on the short list of best lenses I've ever worked with in any format.