Originally Posted by
sard
But the advantage of getting Diamond is...more bonus miles and 2 choice rewards (as opposed to 1 as a Platinum) I would get 2 choice rewards in 2014 and 2 more in 2015.
If you go to DM you won't get two Choice Benefits in 2014 and 2015 -- only two in 2014.
As for more bonus miles, with SM2015 you'll get 2 extra miles per MQD, so estimate your MQDs for 2015 to see how much extra you'll earn.
Your estimate of Gold in 2106 if you hold short is only valid if you make the MQDs in 2015 or have the Amex waiver (assuming it is still there then, but if it's not then a lot other things will have probably changed as well...)
You don't have to fly another airline if you want to hold short -- just credit to AS (though you won't get DL perks).