I personally prefer taking the Disney transportation. This is for two reasons.
1. I'm on vacation, someone else should get to be the chauffeur for once.
I really don't care if it takes a little longer. I enjoy being able to just be the passenger for once. Especially, when we are returning late at night after a long day. By that point, I'm half asleep and staying focused and awake enough to drive around unfamiliar roads is the last thing I want to be worried about.
2. I'm unfamiliar with the roads, and usually end up getting hopelessly lost and frustrated. By the time I finally get where I'm suppose to be, I could have rode the bus and gotten there faster.
My go to plan is drive down, park the car and never move it again until we leave. I love this plan. It works very well for my family.
I don't mind driving around Orlando. I don't think it is really any worse than any other large city, but I absolutely hate driving around Disney. It may just be me, but I always get hopelessly lost. Last trip, I think I went in and out of every park before I finally made it where I was trying to go. I felt so bad telling the CMs at the gate that I was lost and just trying to turn around. I also always seemed to end up in the far left lane when I needed to be in the far right to turn at the next light or vice versa. And the fact that the whole place is filled with just as many lost confused people as me and all the giant buses, just makes it all the worse to drive in, IMHO.
But if you want to give it a try, I say go for it. It can save time when you don't get lost, and I'm sure there are tons of people out there who have better luck and directional sense than me who drive and never have issues. I'd recommend familiarizing yourself with the streets and routes ahead of time though, so you know when you'll need to turn ahead of time and such. That really was my worse problem. I tried to just to depend on the GPS, and hadn't really researched ahead of time, but by the time my GPS told me to turn, it was already way too late for me to get in the correct lane. If I had mapped it all out in advance, it wouldn't have been so bad.