It's hard to say without knowing anything about what you collect! You didn't even explain whether you use the SPG card for hotel stays or for airline transfers (and if so to which airline or airlines)?

Each card earns something different, and every program has a different mix of partners. There is no card exactly like the SPG Amex that's an MC or Visa, so without you explaining what you want from such a card (in terms of what program or programs you're trying to get points/miles in) it's hard to say.