If you really really need a larger car, you can reserve it with the "Emerald Reserve" service---you still get to bypass the counter, but you know for sure that you are getting the car you need. It's more expensive, but very convenient and you can be confident you'll have space.
If you don't *need* a larger car, just go to EA and take your chances. The emerald aisle used to be a great deal, but with the advent of the Executive Aisle (Emerald members that rent frequently) the better cars end up over there more often than not. Getting a larger car (or a cooler one) is strictly a matter of luck, and you shouldn't count on it.
The last time we grabbed a car at MCO, we got a PT Cruiser. Fun car, but actually a tad smaller than a standard intermediate in terms of trunk space---we travel relatively light, so that was okay. There was also an SUV or two on the line, but we wanted style.
On the other hand, my most recent rental (at Charlotte) the EA had 16 Chevy Malibus, all in ugly colors.