The Conductor is, as the name is apparent, the conductor of the Polar Express. The Conductor makes it his number one goal to get the train carrying a lot of kids to the North Pole before midnight. He's a bit of a stern man with deep wisdom behind those motion-captured eyes.
Tom Hanks is an actor who needs no introduction, with this being one of his roles in the movie. He pretty much plays his charismatic humble self, showing off the same charm he usually does for his roles that manages to grab the audiences' attention. While this isn't the most favorite character from his career from me, the performance is lively enough to make you want some hot chocolate too.
Jim Hanks was a natural choice, with this character not being the first time he substituted for Tom. While Jim's imitation of his brother is usually spot on with a few buffs, I think he sounds really put on here in the acting department. I would imagine direction had to do with it, since I've never seen Woody sound so stiff. Still, if you weren't actively putting the two in comparison, you wouldn't have known that it was not Tom, so, props to Jim for still being able to sound like his brother!
Tom Hanks is chugging along on the railroad with my vote.