It really depends on how big your suitcases are and how much other stuff (such as strollers) you need to put in the trunk. Go the rental agencies website and see what kind of cars are in each class. Either research the trunk size on the web or go to a local car dealer with your empty suitcases. Tell them you're thinking of buying the car but you want to know how big the trunk is.
The pp are right, you only need the space to get the suitcases from the airport to your condo but that doesn't change anything, you need enough room to get your suitcases from MCO to your condo. Go to the website and see what cars are in each class. Go to the car mfg website, or a local car dealer, and see how many bags you can fit in the trunk. Alternately get a car that seats 3 in the back. Put a child in the middle and stack 2 or 3 bags on the back seat.
Several of us have observed a families trying to fit all their luggage in a convertible. I left before I found out how long they tried before giving up and requesting a different car. You need a car big enough to accommodate your luggage. Alternately bring less luggage. You'll have a car. You can buy all your health and beauty aids in Orlando. Orlando had WalMarts, Targets, Costco etc. You're staying in a condo, bring less clothing and do wash more often. Most airlines charge for checked bags. You could even use the money saved by not checking 2 bags toward using a wash and fold service at a laundromat.
edited to add you asked what I'd do. Price a min-van and SUV. Book it if the price is right. Otherwise go with a full size car. Plan on stacking some suitcases in the back seat. You might also consider taking fewer, or smaller, suitcases.