In light of recent issues ( #8, #9 ), it appears that it would be easier to actually have control over the default crop options in the WP Admin, rather than just via filters.

Three options could be added for this:

1. Default Crop (fill, fit) - Default fill
2. Default Hard Crop (fill, fit) - Default fill
3. Default Soft Crop (fill, fit) - Default fit

Any additional crops can be added via the existing filters.