Das Reich
What kind of buying guide you are looking for ? Do you mean some sort of Consumer Guide like those they have in the US or the UK ?
There is no better buying guide in the world then the BMW forum. Ask the folks here any questions that you might have. You couldn't find better advices anywhere else.
How do you judge a car is very relative to your expectation. If you intend to drive in a sporty manner, then E46 318i is not the car for you. But if you are contend with a luxury car that handles well and fairly reliable and with good looks, then this is not a bad choice.
To me, the E36 is a better car in many ways than the newer E46. I still miss my old car. While E46 is newer with better refinements...E36 is a superior car in terms of dynamics and reliability.