I used to be a MS Whale. When I was doing it, the best cashback deal I found was BOA with 1.5% base and a 75% bonus if you had a certain amount in BOA or Merrill Lynch ($100K?)

The best value I get now on organic spend is 7.7% This happens if I buy airfare on the Amex site with my Amex plat card, which gives me 5X Amex points, and when I redeem them I get a 35% points rebate.

Of course when you redeem points at a premium (on Amex, Chase, wherever) you are foregoing opportunity cost of points you could earn for the purchase.

Most of my spend is on an Amex card that gives 2x points for - I think, up to $50K a year, which is not a mark I hit without MS. With the points worth a net 1.54 cents after the rebate, I'm getting 3.08% back when redeemed for flights. So if I moved $50K spend to an AA card, I would get 50K AA points instead of $1500 worth of travel. Is that worth it? Not clear.