SAFD - As the Queen of the Catastrophic Disney Transportation Failure, I will forever be Team Car. I always stay off-site so that is the primary reason. But even if I did stay on-site, I would still want control over my transportation.
This may be an unpopular opinion, but I feel like, in general (i.e. not necessarily for race mornings), Disney does as little as they feel like they can get away with. IMHO, they could do a better job eliminating long bus lines if they wanted to put the money behind it. (For example, having a cast member with a radio at each bus station who is able to monitor the lines and getting buses re-directed if things start going sideways).
One mode of transportation that I haven't seen anyone mention yet is ride share. I used it for the first time at Princess this year because I didn't book my rental car early enough and apparently there were no cars available anywhere in Orlando. I was nervous about it, but it went really well. I booked it the night before and left myself A LOT of extra time in the morning (I think I scheduled my pick-up about a half an hour earlier than I usually leave when I drive, which is already really generous). My driver was a wonderful single mother who was eager to chat and learn more about what I was doing at Disney at o'dark thirty in the morning. Getting a ride afterwards was a little bit more complicated (the rideshares were getting caught in traffic so it took longer than usual to be picked up), but I would definitely do it again if I needed to.
The road closures just seem so daunting, even though we are pretty familiar with the roads in property. I know I will be a nervous wreck, worrying I will be late to the race, or miss it altogether, because of transportation!
Honestly, I would worry more about bus drivers who aren't familiar with the roads (the race bus drivers aren't usual Disney drivers and are often from out of town) getting lost. The road closures actually show up on Google maps and I've always been automatically routed around them. And as another person mentioned, almost everyone is going to the same place and once you get close to Epcot, it's pretty much follow the cars. Although maybe not too closely - the only time that I got "lost" (really, misdirected) was when I was following one of the electronic Disney boards and it wasn't quite clear where to go (note: Google maps was clear, but I figured Disney knew better) so I followed the cars in front of me. At least five of us took at loop around the Epcot hotel parking lots before coming back to the same road. It was a less than 5 minute detour.