How do you decide which corpus to use for a new dictionary?

I'm starting work on a new dictionary project and trying to choose a corpus that will actually support the entries I need.

There are general corpora, web corpora, and specialised collections, and each comes with trade-offs in size, balance, and licensing.

How do you decide which corpus is the right fit for a new lexicographic project, and what do you check before committing to it?