I run Mobil 1 synthetic in both the Vette and the SVT and use only Mobil 1 filters (Motorcraft are supposed to be good, but Mobil 1 filters are really top-notch).
The Mobil 1 filter size for the Contour is M1-210, IIRC. They aren't cheap, but are worth it in my limited experience. If you like your car, DON'T run FRAM or any equivalent; that I've heard from a number of sources as well as seen from an independent flow-bench test done on a number of oil filters. They are akin to putting an obstruction in your oil system they flow so bad.
I change anywhere from 5k to 7k miles, depending on whether it's been mostly highway or traffic driving (as well as if I"ve been more abusive than normal as well). Nothing very scientific, I'll admit, but gained from years of listening to folks with more experience in the matter.
