Miami Beach, by a mile. Stay between Flamingo and Lummus parks (between 10th and 15th), so you can roll south and north for eats, take the trolley or walk to Publix/Joe's/Whole Foods, do morning swims in the ocean, and never be too far from transit. Friday and Saturday nights draw the thug element from Miami, and that's generally when you should roll to Miami.
Edgewater is sleepy area that's safe and a tidy. Stay around 27th and Biscayne, where you have restaurants and that nearby, and good transit toward downtown and transfers, and so you can walk over to Wynwood.
Brickell is probably third. By far the best transit in all of Florida. You should probably stay here near Brickell City Center, which is great. The Uruguayan restaurant Parador La Huella had a Miami outpost that's just insanely good. They even import the beef from down there. Staying near City Center is great because you have access all of Brickell, downtown, and bus routes to the Beach and elsewhere, including SW 8th Street aka Calle Ocho, which is the great high street of Little Havana.
Nowhere else is as great. Post again once you're there and I can fire a laundry list of great places to eat and drink.