If you fly Delta 85% of the time or more I'd go with the Amex:
-gives you another free bag incase you need it
-earn 30k mqm's (if you spend 60K on the card)
-tiebreaker for upgrades
-access to skyclub
Extra bag is a rare perk I would use. (not to mention the platinum card gives you $200 in incidentals on airlines each year)
I am not sure that I ever spend 60k on a card, so I might possibly be chasing something that wouldn't be possible.
Tiebraker would be nice for upgrades!
The sky club is a primary reason for me getting one of these cards. Added bonus that platinum does allow for other clubs as well.
Very tough decision.