The 166 pushed Alfa into the big executive-car space with real Italian limousine style. That also means it should never be bought on charm alone: on a 166, front suspension, cooling and automatic-gearbox condition matter immediately.
The `2.0 Twin Spark` is the entry point but still needs careful oil and ignition reading. The `2.4 JTD` is the logical mileage car if intake and turbo work were kept up. The `2.5 V6` and especially the `3.0 V6` bring the smoothness and voice expected of a large Alfa, but demand serious cooling and leak vigilance.