For me it's the destination. The first hour of the road trip is fine, but every hour gets progressively worse and worse until you're at the last hour or so when you're almost there. But depends where you're at, I live in Vegas so anything 3 hours within here is gonna be desert with boring small towns. Once there's a change in terrain or the desert simply looks different it gets interesting.
I kind of thought of this as a different way too, that you may not have been actually meaning road trips. Like you meant reaching a goal or something. In that case, I say the journey is more important because you learn from past mistakes that didn't get you there that'll help you next time.