Napoli is not healthy to start the season - I would downgrade him on this basis. The Angels are saying he will can DH to start the season even though his shoulder will be too lousy to get behind the plate, but I think we all know to be a little circumspect about claims like this - there is a risk factor here.
As for Molina, keep in mind that he is 35 years old and does not exactly have a stellar track record of playing 130 games (last season aside) Yes he will put up nice counting stats hitting clean-up, but there are both health factors and age factors working against him - in aggregate these ammount to a big risk. I am not aware of too many Cs who maintain strong performance past age 35, and I would be pretty surprised if Molina (and Posada for that matter) are in the top 10 at the end of season.
When is comes down to the scrub Cs, I would rather go with someone like Navarro or maybe even Y Molina, who will not produce as strongly as B Molina on a game-to-game basis, but has a much greater chance to maintain health and current level of performance. I do not expect Y Molina or Navarro to duplicate last season's BAs (I am aware of the BABIP issues), but I still like them to provide better total value than B Molina when all is said and done.