Take a look through this:
http://www.myturbodiesel.com/buyersguide.htm
If you're looking for the mk4 body style, then they are pretty much the same in use. The later cars have a little more power and you should expect a little less mileage. Manuals get better mileage than autos. The whole oil thing is a touchy subject. There are a lot of scaremongers who will tell you that your car will blow up if you use the wrong oil.
The fact is that you should use VW approved 505.01, 506.01, or 507.00. The price difference is minimal, it's got the additive package that the engineers designed for the car, and it will keep the warranty intact. It's also a fact that the car will work with non approved oil but for the above reasons, I don't recommend it. I give conservative recommendations and I don't know enough about the various oils to say that "x" oil is okay to use. I do know enough to say: why would you not use the approved oil?
The passat should be fine, it is a pumpe duse engine, all 5th gen passat tdis in the US were. 3000 miles is a short change interval, 10,000 miles is fine if you use a quality synthetic. The best car for you really depends on what your budget is and what kind of deal you can get on it. I'd say that over $20,000 is too much for the passat. Under $15,000 is a very good deal. Somewhere in between depends on the condition.