Depends what you principally care about. I'm aware SPG is relatively poor in terms of absolute points earning and free nights, but that really doesn't bother me as I'm not looking for a hotel loyalty programme purely for the most free stays. What I care about is excellent top level status treatment at high quality hotels, which SPG gives in spades (as far as I can see Hyatt is the only other major chain that comes close).
I'm sure some people will be happy for SPG to move to an 'earn and burn'-type loyalty programme, but if I were just looking to get as many free stays out of a programme as possible I'd focus primarily on IHG again with it's constant large bonus points promotions.