They earliest TH ADR is I think 8:00AM. My girlfriend and I had an 8:15 ADR, we were out by the bus at POR by 7:20 just to be safe. The timing ended up working out great since we didn't feel rushed walking fromt he gate of AK to the restaurant. We love ADR's that are either before the park opens or let us out after the park closes, it makes for very peaceful walks and great photo-ops without many people in the way. I believe the buses start to run an hour before the first ADR.
CM's is basically the same deal (not sure what time the first one is). Take the bus from POR to MK, then walk to CR. As a rule of thumb, we give ourselves about an hour to get from point A to point B. It usually leaves us more than enough time and we don't ever feel rushed.
As for which is better, TH or CM, my girlfriend and I are split. She insists on CM's and I liked the overall experience at TH better. In the end, when it comes to breakfast, you really can't go wrong.