For a Passat I would want to make sure any warranty covered injectors and issues (if diesel), turbo and ancilliaries (prob not cover the actual turbo fully), gearbox (especially if dsg), and electric brakes amongst the more general mechanical items. Ask specific questions to get precise (written) answers on coverage of items like these.
Also be sure how the warranty works, will most garages accept the warranty company, some won't pay full garage rates and garages will refuse to work for them. Is it a pay out and claim back type, or they pay the garage direct?
No personal recommendations for any warranty company, but some are better to deal with than others.