@evan
It’s a vague question because it neglects to establish whether the train system is well implemented or the garbage such as what you have in most of the US.
Considering it’s an international poll & you don’t know where responders live, we have to make assumptions. What if an American visits Europe? Should they answer in terms of travel from home, or within Europe?
I move around, so I have a different preference with each place I find myself. Then I also have a preference of fast trains in a hypothetical region where all forms of transport are at their best. But even that’s not a simple answer, because pricing affects my preference. Sometimes the fast train is /cheaper/ than the slow train due to marketplace idiosyncrasies, but not typically.