Another way to think about this question might be "What US territory is closest to the equator." There are definately better options that Florida, but they are outside the continental US. Obviously using these sites is a bit of a trade-off since it's not as convenient to the rest of the industrial base.
Here are the latitudes of some possible alternates:
Cape Canaveral: 28 degrees N. Hawaii: 21 degrees N. Baker Island: 0.11 degrees N.
Baker island looks best on paper, but it is just a tiny nature preserve, not practical for large-scale rocket use.