I think the vast majority of trains will go electric. This is already a mainstream technology (unlike electric cars). Overhead wires or 3rd rails in most places, with batteries where that's not possible or economic. Perhaps hydrogen will have it's niche though (perhaps on low-use railways?).
Hydrogen fuel cells and batteries are roughly comparable technologies.
The main difference is that you can use the power grid to "charge" the fuel cell while it's in motion. You simply generate hydrogen at its destination, then rapidly pump the hydrogen into tanks when it stops.
So, the higher the duty cycle of the vehicle, the more sense hydrogen makes. Also, hydrogen has higher energy density (volume and weight per unit energy are both lower).
For those two reasons, I'd guess long haul, heavy use lines would be the first use case for hydrogen, and that batteries won't ever be particularly competitive for those use cases.
Hydrogen also requires quite a bit of infrastructure that hasn't been built out, whereas railways generally have an electrical supply already. I suspect that will make batteries a lot more competitive in the short term. Hydrogen could make sense if it can overcome those hurdles. But with improvements in battery technology (solid state lithium batteries seem to be coming soon) I wonder if it will ever be better enough to gain adoption.
