From my experience, the best kind of image to import into Toon Boom Animate for vectorization is a PDF file.
Here is my scenario.
I exported an image I drew in Toon Boom Studio and saved it to different images types (bmp, jpg, png, tga, pdf).
Next, I imported every image onto its own layer in Toon Boom Animate (Black and White and vectorization).
I then played around with each vector image and came to the conclusion that the PDF was the best to work with. Here’s why.
When I select the entire image, the ‘pencil selection’ property under ‘Tool Properties’ shows up to change the thickness of the lines which tells me that the PDF image retained the fact that I drew the image with a pencil and not a brush in Toon Boom Studio.
Why is this important to me? After selecting the entire drawing and then flattening, I can mouse wheel click each stroke and it selects only the stroke that I clicked (For cleanup purposes). The other imported images would end up selecting more than the line I cared about. Why did it do this? Again, because it appears that even though I drew the image with a pencil in Toon Boom Studio, all but the PDF exported the lines as a brush stroke.
Now, I could have converted the lines of the other imports from a brush to a pencil stroke in Toon Boom Animate, but it distorts the drawing a bit. That’s no good.
The only extra step I had to do though with the PDF import drawing was increase the thickness of the pencil lines. For some reason, the PDF export did not retain the pencil thickness. No big deal.