Having used face unlock, it's really gimmicky. I turned that off right away. It could be a good idea in the future but, like with Samsung's hands-free gestures, right now I'd have to spend too much time aligning my face and waiting and hoping that it was going to work.

Touch ID takes what you would have done anyways (thumb on home button to wake and then type in PIN) and makes it even faster. Now you still put your thumb on and eliminate the typing pin part.

I haven't used Touch ID yet but I wake my phone a lot during the day, so this seems like a nice (but not absolutely necessary) feature for me. Something small that makes the experience that much better.