A finger sucks in just as many (albeit fundamentally different) ways for mobile usage. So what we have here is a discussion about preferred suckage. And let's stop right there.

Now that we have all that covered, let's get on to the real deal, pupil-tracking pointers. Fast, no hands needed, does not obscure the screen, high resolution and much more uniform among human population than fingers. We just need a higher resolution user-facing IR sensitive webcam.