I'm probably a WDW vet by normal people standards, but certainly not compared to WDW superfan 30+ trips standards
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Yes, I always drive. It works out great everywhere except MK, where your decision to drive will add ~20 minutes to your commute because you have to board the ferry or monorail at the TTC to get to the park. Nothing against the buses, I just don't like giving up that level of control on my trips. If I'm going to be late, I'd much rather it be my own fault than to have it be because of transportation mishaps or bad luck.
I think the consensus is that the buses have gotten a bit better and more responsive as of late, but I've heard far too many stories of people waiting for an incredibly long time and/or watching bus after bus come for a park they're not going to while their own bus is MIA. It's a risk I'm not willing to take, especially since rope drop is so much more important at WDW.
As for the most fun way, I'd probably say anything but the buses or your own car. My first trip we stayed at the Dolphin, and taking the boat to the Studios and Epcot was really cool. The monorails WOULD be really cool, but they're from 1986 and desperately need to be replaced (a lot of people have complained about smell and cleanliness too, but I have never personally experienced issues with that). I'd give special kudos to the Epcot monorail for the nice sweep it does around Future World before you exit to go to the park. The MK ferry is probably the single best method though, and as much as it's a pain to deal with the TTC, taking the ferry to MK for your first visit is probably the best, most awe-inspiring approach. And frankly more peaceful, as most people's instinct is to take the monorail in that situation, which is...not fun when everyone has the same idea come closing time. There's a reason no other park has that setup. I haven't done it, but the Skyliner looks cool.
And since there's no direct cost to use any of these systems, since none of them enter or exit inside of a park, you could theoretically ride them to your heart's content!