You will get marginally better mileage in the Jetta.
The real decision will boil down to other considerations: how much room do you need, do you just like the kewl looks of the NB so much you can't stand not having it, are you worried about resale, do you need 4 doors, do you have to have the car now and must take what's on the lot or can you wait for exactly what you want.
Personally, I needed the back seat, 4 doors, and thought a Golf would do me better than a Jetta. The NB just didn't have the rear seat and trunk room I needed. But that's me.
I also do 110 miles round trip each day, 85% interstate cruising at 71 mph indicated. Unless someone decides to have an accident, then it is a very long parking lot. Anyway, I get 51-52, up to 53 so far if the weather cooperates.
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Always interested in steep & deep.
Ski resorts closed! Break out the cameras and fly rod ...