The buses are much easier for getting to MK than driving would be - as stated above, you have to park at TTC and then either take a ferry or the monorail to the park gate itself, whereas the buses drop you off very close to the gate. The main downside to buses right now is that, for people who want to be the very very first ones into the park and sprint back to one of the coasters, you can't do that by bus. The other consideration is being on a bus with other families, but honestly if you're ok being in the park and on rides with other families I think it's not different enough to skip the bus given how they are currently handling/loading them. (That's just my opinion and obviously everyone needs to do what they are most comfortable with and what they feel is best for their families.) If it were me, I would recommend the bus for ease of use and closeness.