Looking for a recommendation on a used car to start commuting longer distances.

I am looking for a recommendation for a used car under $20,000 that I will be using mostly for commuting ~70 miles daily. This will be almost entirely on highways.

I currently have a 2007 Audi A3 and like driving this car, but it now has 110,000 miles on it. Although I have taken great care of this car, I am reluctant to have to rely on it for longer daily commutes.

I have been looking at some fuel efficient vehicles, hybrids and electric vehicles. I thought for a long time the Chevy Volt would be a great commuter vehicle. I could charge the battery at home and possibly at work as well. That way I could make the 70 mile round trip on all electric.

My second car I have been eyeing is a VW Golf TDI Wagon. This gets great fuel mileage and I like the idea of having a wagon. Plus the torque of a diesel would make it more fun to drive.

Both of these cars are within my budget and I like the idea of driving either one. I realize there are other fuel efficient cars out there, but there are also many that seem extremely boring to drive. I have loved the quick little turbo Audi I have now and I don't know how I would feel about a car without decent torque.

Would you recommend either of these cars? If not, do you have any recommendations that fits my criteria and would actually be fun to drive.