I use masking tape because it doesn't tear as unexpectedly as transparent tape. Once a tear starts with transparent tape, it quickly goes all the way through. Plus, transparent tape, for me anyway, is harder to completely remove from the spool and film than masking tape.

That said, and while it may not be a big issue for this use, masking tape definitely deteriorates with age. I learned this from using it for its primary function, masking. Old masking tape starts to curl at the edges and loses its stickiness. Sometimes stores keep their masking tape for a very long time, so make sure you are buying fresh tape. (Especially if you'll also be using it for painting your car or house! )

While I'd use Duct Tape for just about everything else, I'd never use it for taping film to spools!

-chuck