I'm using my SPG card for all Marrriott stays at this point, because I'm am several years away from lifetime Platinum status at this rate, and the lifetime requirements are extremely likely to change in the next year or so (and/or SPG lifetime metrics likely to start counting in the next year or so). I might apply for the Marriott Business card soon, and if so, I'll shift for 3 months to that, but then back to SPG after that.

So if you're much more than a year away from the lifetime status you seek, I recommend the same, choose the card which earns more (the SPG card, unless you're doing a singup bonus on a Marriott card), and don't worry about how to achieve lifetime status until the new program is announced.