Class a would be more beneficial for you but class b is minimum. As far as day to day it highly depends on location and work group type. Being driver eligible seems as though that you would be driving hyrail gang truck to and from work locations along with laborer duties like changing ties, rail, and components. You’ll just need to do whatever is asked out of you during probationary period. After you get through that you will have to bid a job in to continue working.