What about other options?
They aren't options
We try not to think in "TFDi" and "Carenado". Having nice models at hand is a part of the considerations but by far not the whole thing.
There are tons of airlines that fly everything just because a model has been released. That's fine, but it's not the way Metro operates.
Oh and by the way, the Q400 is clearly my first choice. Especially for this particular project