I am in the rent a car camp - for a few of reasons.
1. I take public transportation every day so if I am on vacation having a car is a luxury I am willing to pay for (although I thoroughly search discounts and deals to get get a good price).
2. My kids nap in the car so we will leave the park in the afternoon - drive for a while and get them to fall asleep and then go back to the park with refreshed and happy kids.
3. We like the freedom of being able to go to the grocery store and the Disney outlets.
4. I remember the first time I went to WDW with my husband (boy, he didn't know the Pandora's box he was opening when he gave me a trip for Christmas). The cast member told me to allow 1.5 hours for travel time to get from the Caribbean Beach Resort to the Contemporary for the Chef Mickey's breakfast if we were using Disney Transport. I was shocked, at which point I asked, well, what if we have a car. Oh, then it is only twenty minutes. SOLD!!!
Ever since we have been a must have a car family (with the exception of one trip with a friend who doesn't drive, and although it wasn't bad, I will admit I didn't enjoy waiting for the buses.)