An Audi for that time period was essentially an AWD VW with more convenience electronics. The interior styling of both are a matter of preference. A B5 4Motion Passat is basically a Passat body frame laid on a C5 Audi A6 chassis (same drivetrain, 2.8 motor, etc.) The A6 would allow you to also choose between a 2.7t (V6 biturbo) and 4.2l V8.
If you compare Audi to VW now (ie. the present,) you get a lot more deviation. Audi has emerged as the luxury brand that VWAG has probably always intended it to be. Audi's also continue to have much more complexity like four link suspension, independent rear suspension, quattro, etc. then any VW (minus maybe the Touraeg.) In the meantime, VW is still deciding whether or not it will offer more for the layman's VW.