Orlando is just that, Orlando! Its set up is pretty much for tourists... International drive is a handy location for staying and you can normally walk from your hotel to close buy restaurants... mostly chains like TGI / Ponderosa / Aussie steakhouse... but they are exactly what they say on the tin.
Shopping in Orlando area is pretty decent, you will find the main US brands in the outlets around international drive, Belz and Premium Outlet, both are easlily reached by the I trolly, which goes from one end of I Drive to the other.
Miami is not one of my favourite cities in the US, personally I feel that there is a very 'transient' feel to the entire place, like people are only there until they get on their feet and can move onto somewhere else!
Personally I much prefer Fort Lauderdale just up the coast from Miami, it has a more settled feel to it, and feels a lot safer to be out and about in.
Whether you go to Miami or Fort Lauderdale, I would recommend a trip to the Sawgrass Mills outlet, it has some great stuff and I would recommend checking out the clothing in Target, there are some good designers working for them. At Sawgrass you can do the movies, as they have a nice complex, but if you decided to go and see a movie make sure your car is close to that exit ;-)
the only other recommendation I'd give is don't bring much with you except for space! Bring a couple of days worht of tshirts/shorts, and buy the rest!