Performance question - Animations in spritesheet vs animation in Mecanim?

I am determining for an image whether it would be better in terms of game performance to (A) create the completed animations in something like Spriter Pro and export to a spritesheet the completed image frames, or (B) import the sprite "parts" to Unity and build the animations using Mecanim. In terms of getting the animation working, it may be a moot point (either way works), but which approach has the least impact on game performance.

Using just a spritesheet of the completed animations might take up more memory, as the image content is repeated a lot in the many frames, and the number of potential frames could grow exponentially for a variety of animations, but for a small number of animations, I would think just animating through a spritesheet would be faster.

Thanks in advance for any input.

Kelly Strouse