1. It doesn't matter. 2. Optical is better. 3. Coax is better.
My opinion:
Coax is better. Optical connections are very cheap to make and include in a system. Most devices have them now, but not all have coax connections because they're more expensive to include.
Coax has about a 100 times higher dynamic range than optical, and generally has less jitter.
One detraction to coax is that it grounds the player to the receiver which can induce a hum.