Our 54 plate Mondeo 115bhp TDCi has done close to 120k and returns an average of 51mpg with mixed driving(mainly on country B-roads,motorway driving is more 60mpg territory but we very rarely do it).I don't want to tempt fate,but it has been pretty reliable bar a failed water pump/power steering pump assembly (a common fault on these) and a split
hose.It's a well built,solid car,but no matter what I do I can never be 100% comfortable in it,and it does have a few strange foibles like the fact that it is very easy to stall when pulling away and the steering tramlines over certain types of roads.
The Saab diesel is basically a Vectra in disguise,and is probably not made as well as a comparative Vauxhall.Saab have been through a fairly rough patch build quality wise,and the early 2 litre and 2.2 diesels are painfully slow.
The Renault Laguna 2 dCi is.....erm.....well,just have a search around the forum.
This is my own opinion,but I would think that the Mondeo would be the one to have,but I'd have a look at a Honda Accord and a Mazda 6 before going too far.