This is definitely a matter of personal opinion but I MUCH prefer driving myself.
We took the busses the first two days of our last trip (first time onsite) and then never got on them again.
It depends on where the bus is for your particular resort but it was a closer walk for us to the parking trams than to the bus. The line for the trams wasn't as long and moved more quickly than the one for the bus. Once I got to my car I was able to 'board' immediately, I was guaranteed a seat and no one was standing over me or squished up against me and I didn't feel like a heel for not giving up my seat to someone else. No one was bumping me with bags, backpacks or strollers, no babies were crying and I could listen to the music I wanted to.

If I wanted to hit the convenience store or mcdonalds drive thru on the way back, I could. Back at the resort, the parking lot was much closer to my room than the bus stop. Driving ourselves was definitely a win, win, win for us and we usually got 'home' faster when we drove than we did when we used the bus.
Disney property has excellent signage and maps are available. We never had any trouble finding our way around. Parking is free if you are a resort guest.
We drive to WDW so we have the car anyway. Even if I had to rent one I'd still want a car, though. I'm not a good bus person.

Others love it, though. I can see the value of the buses for MK since you can't park there but the trip from TTC to MK is our time to ride the monorail, which we enjoy.
One other bonus of having a car...if you plan on visiting any other resorts for a meal, shopping or sightseeing, you have to take a bus from your resort to central location (TTC, DowntownDisney) and then catch a bus to your destination resort. Time consuming and tricky to plan if you have to be somewhere for an ADR.