@Katie2980 , Whether driving or using Disney transportation, each option has its pros and cons. A few thoughts below, and I'm sure that other forum members may also have some good points to share with you.
Some guests enjoy driving their own car, because they enjoy the freedom. It may also be faster in certain respects, but keep in mind that the WDW parking lots are huge, and you'll have to wait for a tram to take you to the park entrance. (The trams do run often; although, if you wait until park closing time when the crowds all depart en masse, you'll be waiting in queues to get on a tram, to return to your car in the lot.)
Other guests (myself included) prefer to use WDW buses, monorail, and boats. I like to totally relax on vacation and am comfortable letting those CMs in transportation handle everything. Overall, I think they do a great job, and the wait times between the modes of transportation (buses, monorail and boats) are reasonable. Also, Disney transportation takes you directly to the front entrance of each park, (so no additional tram ride from a parking lot is needed).
Lastly, some guests elect to do a combination of their own car some days, and Disney transportation on other days, depending upon the specifics of their schedule.