Same here. I've kept PLT at MR and SPG since 2002. I've been in multiple locations where only one of them was present and very rarely has there been neither of them.

Marriott certainly is more prevalent, so that would be my choice if I had to choose only one. But SPG's real "if there's a standard room available, it's available for reward redemption" is still quite valuable, even though the earn/burn ratio is worse.