At that time of the year you are likely to run into 2 issues: Major heat haze and poor lighting because of the position of the Sun. So early morning and late evening are the best times to venture out to MIA
then. That's not to say you can't get some decent shots otherwise. It's just that it will be more challenging.
Personally I prefer the El Dorado spot because the planes are closer which helps with the heat haze and it's a more comfortable spot to shoot from. At The Holes they are further away and because the runway is not quite level in some areas, the wheels are often covered half way which can destroy an otherwise perfect shot. Again just my opinion, there are others who will disagree and I have seen some great pics from there. I guess it won't hurt for you to check it out anyway.
The 2 spots above are particularly good for westerly landings. If they are coming in from the east, then you will probably need to drive along Le Jeune Road (borders MIA
to the east) and find a spot to sit in one of the side streets. Or maybe, visit the famous 94th Aero Squadron restaurant that runs along The Perimeter road. They have a huge parking lot that you can sit in.
Easterly landings are not my favorite although I have gotten some great shots along Le Jeune Road. You can sit at El Dorado and catch them flying over, but they are usually very high unless they are heavy. I've never visited The Holes for easterly landings so can't comment. However, I'd imagine it's a similar situation. Just my 2 cents and good luck!
Nikon D7000 / Nikkor 105mm AF f2.8 / Nikkor 35 f1.8G / Nikkor 50 f1.8D / Nikkor 85mm / Nikkor 300mm f4 AF