For interesting TLs, if done plausibly, a United States that never quite crystallizes for a variety of reasons - that is, you've got your same base British Colonies, but for whatever reasons they don't unify into a United States, at least, not as we know it. Also, the establishment of independent monarchies, at least in the early period.
Essentially, anything that shakes it up so that independence does not happen as OTL, but once the U.S. has been formed fully as OTL, I prefer it to mostly follow the path of OTL - westward expansion, continent-spanning (though maybe not quite as continent spanning, or expanding in different directions, so on) and a major world power - though not necessarily a superpower.