I think I know the answers, but thought I would start this thread. For me, until the end of 2015 (and maybe during 2015 to keep my lounge access before Delta (and Amex) become useless for me, I will mainly use my Amex Skymiles Reserve card. When it comes up for renewal in November 2016 I will not renew it unless Delta has made changes (highly unlikely). The good timing for me is that my travel this year will still result in Plat Med Elite Plus status, and I can use the Amex card for the benefits it provides flying Delta. When those benefits from Delta begin to evaporate in 2015-16, I am planning to use Chase Sapphire Elite Mastercard almost completely, and will probably cancel my Amex card. I will keep my Marriott Rewards card, despite only 1-2 stays a year, because it has the international chip and is relatively inexpensive.
Today I got an invitation to join the Black Card VISA. It makes it out to be hotsy-totsy (excuse my language, but I am originally from a lower middle class family) but with a $495 non-waived fee for the first year it is much more expensive than my Amex reserve card. And one review pointed out that to get your first reward after spending $1500 and getting a $500 ticket, you could have just bought it anyway?
Any thoughts? My personal favorite without the Delta perks is Sapphire.