For most purchases I'd agree but I think this one is debatable. He'd get 5 MR points per dollar spent with Amex Platinum vs. 3 UR points with CSR. While in my experience SkyMiles are worth around 1 cent each [corrected] unless used very carefully (and with a lot of hunting), MR points can often be worth a lot more than that with other transfer partners. For example, if the intent were to transfer to BA, then the MR points would be a much better choice (5 BA points per dollar spent vs. 3). BA has relatively high fees on premium class redemptions, but great availability compared to all the US airlines. So these kinds of uses might make sense for some people.

I would definitely not use the Amex Delta card though...