Comes in different size too
Actually the Bombardier design is the most flexible. It has a better turning radius, and is truly modular. It comes in many lengths as well (see Brussels and Edmonton for longer models) and each extension in length uses the same parts. You can keep adding length by just adding two additional modules that are not unique by design.
If you look at the Citadis there is a unique single truck middle module for the short length, a different longer double truck middle module for the medium length, and another one truck middle module for the longer length.
That said, the better design of the Bombardier equipment means little if they don't actually deliver them.