Hi Peter,
I did see workshop scenarios for M-GP for freight and you can run locos like the DB BR103, DB BR111, DB BR420 etc on it, which all have excellent realism and scripting.
So if this kind of German content is your thing, and you have some of these trains already, I'd say, go for it!
However, the Settle to Carlisle line is a great piece too, I love the feel of driving over the S&C, and besides diesel freight hauling you also get all kinds of Steam Specials over this line. Oh, and it brings back memories of those times in MSTS
Choice is yours, of course - I have the S&C for a while already and got M-GP when it came out, both are great value, but recently I've been more into German stuff.
Good luck making a choice but I'd say that either way you can't go wrong!
--Tim