Ritz-Carlton and Hilton promotions are most generous, and Hyatt promotion least generous (how IHG shakes out depends on what you’re targeted for). All require registration.
It’s always worth registering — goodness knows I find that my hotel plans aren’t perfectly predictable, I wind up staying places I wouldn’t have expected, and I don’t remember to go back and register later for bonuses I might earn. It’s best to take the time all at once to do it.