This being my first post on the boards, I can't post links.
If you really want more information on a specific VW, I'd highly recommend checking out VW Vortex (forums.vwvortex.com). There are other forums out there, but "the 'tex" has the larges community and has specific forums for models and their generations as well as forums dedicated to a specific engine since they're shared between models. If you go diesel, the TDI Club (forums.tdiclub.com) forums is also a great resource.
To add to some of the comments here, don't let the premium gas requirement be a deterrent. If a VW/Audi engine specifies premium, put premium in there. It can handle lower grade fuels, but it will only retard the timings after the knock sensors detect it knocking. You will also get less fuel economy with regular gas in one of their engines designed for premium.
Factoring fuel costs and efficiency for my 3.2L VR6 BJS engine, it costs the same and at times less with premium due to better efficiency. Given that and the damage knocking does to an engine, I don't have a reason to not get premium.
The turboed VW/Audi gas engines are easy to tune and can get a bunch more power from an ECU flash. Their diesel engines can also benefit well from an ECU flash, but may not be the best idea if you have a lead foot since diesels already have a bunch of torque.
If you're looking for high fuel efficiency and longevity, go with the diesel. They last longer and are more simpler in design. To meet the newer emissions regulations, the newer engines inject a fluid called DEF into the exhaust which will need to be topped up on occasion. If you do get a car that uses DEF, don't bother with the dealer filling it up; it's a non-toxic solution that's easily handled. Also, some diesel cars that use DEF won't start without it so factor that before purchase and having a small extra bottle in the trunk should alleviate any concerns.
Another benefit to Diesel is one can put in straight vegetable oil (SVO) in an emergency or some modification when going full time. The manufacturers generally don't approve of this, but most people that own diesels consider it safe in warmer climates. Colder climates require SVO to be warmed up since it will gel below a certain temperature. Used vegetable oil (WVO) needs to be filtered of contaminants and may require additional modifications over SVO.
Diesel is surprisingly an efficient fuel and engines can go past a million miles with proper maintenance. I've read some people with Beetles and Mark IVs able to get past 60mpg hypermiling with 40+mpg daily when driving quite conservative. Talking about longevity, there was a guy on the TDI Club forums that went past 600k miles; though, he did have to replace the clutch and 5th gear a few times. TDI Club has a great FAQ on getting the most out of the engine.
I would stay away from the FSI gas turbos (TFSI and TSI branded are fine) and the Pumpe Düse diesels (aka PD-TDI) as they have an engineering flaw with the Cam Follower that needs to be maintained. If you're handy working on engines, replacing the Cam Follower every 50k isn't a whole lot of trouble, but if it not replaced, it will fail and cause more damage. VW has increased the warranty on these engines as a result, but that warranty only goes so far.
If you plan to keep a VW or have multiple VWs and maintain them, investing in a VAG-COM from Ross-Tech (ross-tech.com) is a good investment. They reversed engineered VW/Audi's communication protocol so their tool can talk beyond the government mandated OBDII protocols. One can run diagnostics on almost everything, even the radio and AC. Modifications are limited to a handful of items on K-Line cars, but CAN-bus cars have more options with longcoding. If it's a CAN-bus car, the cheaper Micro-CAN cable is fine. If the car is K-Line, you'll need the more expensive ($100 more) HEX cable. There are Chinese knockoffs in fleaBay, but they use older software from years ago. When shopping around for used cars, this cable is handy since it might tell you there's a major problem with it before you bother going for a test drive. When shopping around for my wife's car, the diag showed that this one car had issues going into 3rd gear on the automatic trans; a test drive confirmed the diag. If you don't want to invest in one, there may be someone local that's willing to do a diag for you or lend you theirs; most people request a six-pack or lunch in return.
Yes, I am a VW fan of sorts, but I don't claim they make perfect cars. I enjoy how well most VWs handle and the torque from their engines; most other manufactures just aren't as fun for me even as objective as I am. Every manufacturer, Honda and Toyota included, has their problems. Regardless of what brand you buy, never get the first couple of model years in a new generation of car. It's best to get the last year in a generation since they should have worked out all of the bugs by then.