As a general rule, the USA uses a 'first come, first served' policy for the use of its airports. You are free to fly into any public use airport you like, with few exceptions. Fill yer boots with large international airports or small local ones, whichever takes your fancy.
The GA facility at KMIA is there for.....GA! And to collect the county fee, of course. But no flashy building, lounges or other FBO-type services. Load & unload your pax and have a piss is about all that's offered.
Just a thought though: Is KMIA the nearest airport to where your pax need to go or come from? There's a large number of airports up & down the Florida coast, including around Miami, so KMIA is not necessarily the most convenient.