This is a no brainer for me...Tamiya's Dragon Wagon. In addition to the kit itself, I have three sets of PE: Vehicle exterior, Vehicle interior, and the Trailer. It's going to be a monster whenever I decide to tackle it.
There are a couple close seconds though:
Tamiya's Tiger I Late with the Eduard PE exterior set and three Verlinden sets: Interior, Engine Compartment, and Exterior details.
Tamiya's Famo with Trailer including the Eduard PE set for the Famo and both of Aber's PE sets for the Trailer.
Enjoy your modeling...