Depends upon what you like to do ,Things to do in Miami and the surrounding areas:
Things to do in Las Vegas and surrounding areas
As far as the heat, it is a matter of preference, would you rather have hot humid heat like in Miami or would you prefer to feel like you are in an oven in the dry desert heat?
Hurricanes or earthquakes?
In both cases, air conditioning is a must. One thing I didn’t like about Florida is that there are no mountains, but there are no beaches in Las Vegas so decide which you would rather have
hiking or fishing?