There are several good Giant Bicycle dealers in Southwest Florida. Go in and scope a few out. Tell them what you are up to and have them assess your needs and match them to a bike. If you have an athletic past a flat bar or drop bar road bike might be the ticket. If you have no background in exercise, then a comfort bike could fit the bill. Keep in mind the object of the game is to enjoy riding so that you do it consistently and desire to do it more and for longer periods of time. This means that you have to be comfortable when riding. Eventually you outgrow the bike and move into something more suited to a new level of fitness and goals.
FYI, I still ride my comfort bike on short errands or when I don't want to put all the gear on for a longer ride. That bike gets ridden several times a week!