Well, there's tons of small towns in the US that only have hotels in Choice and/or Best Western and/or WyndhamRewards. So if you really want to have just about everywhere (that has points-earning hotels in the first place) covered, it's one (or more) of these that you may need to belong to. (However, of those three, only Choice has near-perpetual "rich" promos that -- at least if your stays are very short -- earns you more points faster than in just about any other program.)

As for Hyatt, it's not a backup program for SPG, rather it's a program which has such a small footprint, that some people who have Hyatt as their primary program use SPG as their backup!!!