In terms of course content, Lancaster seems a lot stronger, which a much greater emphasis on modelling. Having a project is a big advantage too.
Looking at the FT's MSc rankings (
http://rankings.ft.com/businessschoolrankings/masters-in-management-2011) The schools seem modestly similar, but Manchester has the edge on almost everything, including salary. However, Lancaster students rate their placement service more highly.
LUMS is a well respected school, but Manchester clearly has a much larger and stronger alumni network.
I think a lot of this choice depends on you. Personally, I think I would opt for the Lancaster course because of its better content and more positive careers service, however you'd need to build personal momentum to make up for the (slightly) weaker brand recognition.
PS See also
http://www.find-mba.com/board/23096/1#post-23293