My 2003 Volkswagen Jetta GLS TDI has performed flawlessly thus far. I've owned it for almost four months, and have put about 6,300 miles on it during this time.
I'm a tall person, and previously owned a very spacious sport utility vehicle which was very comfortable, but returned only 13 mpg in my city commutes. Although this car was in perfect condition, I found the fuel economy abysmal, and the preventive maintenance requests excessive. I began looking for a car that would be considerably more economical.
I looked at the Toyota Prius and Honda Civic Hybrid. Although both reportedly get great gas mileage, I found both rather dull. There was insufficient leg room in the Prius driver's seat for me. I also thought that the Prius' instrument panel was unnecessarily "unique."
The Jetta GLS TDI was an excellent alternative. Mine gives me between 39 - 47 mpg in city driving, and thus far between 42 - 50 mpg on the highway. It's extremely comfortable up front, although space is skimpy in the rear (as it is with most cars this size). The trunk is absolutely huge, and with the rear seat folded down, can hold nearly as much as my former SUV did. I wish I'd purchased this car much sooner!
I have a 2003 Jetta Diesel. Since I drive quite a bit (in 18 months of ownership I have 50,000 miles on it), I can only speak highly of this car. I only get the oil changed at the dealership, I am wary of taking a diesel car to a "Jiffy Lube" type place. The dealer charges a whopping $60.00 for a synthetic oil change (Jiffy Lube here charges 24.95), but the fuel savings make up for it. I average 50 miles MPG without the A/C on, and have averaged about 42 MPG with the A/C on constantly. The power is fine, and is easy to start in the winter.
My 2003 Jetta TDI has been absolutely wonderful so far with 51,000 miles. I have required no unforseen repair costs other than recommended maintenance (synthetic oil change every 7500k). Averaging 47 mpg mixed city/highway. While the vehicle was assembled in Mexico, I have found no compromise in build quality!
2 aspects I would suggest improvement. Stiffer suspension and thicker sheet metal (dents easily). Other than that... a fun car to drive!