B+D joint first with C runner up.
B+D:
In some places trains are too short, & certainly not enough units imo. I'd like to know what is so wrong with some of the trains we build that when we finish building them, we wait for a few years or a decade & move on to the next class? Trains today are 'modern' enough to suit peoples needs, what wasn't acceptable was the slam door stock with no central locking, so I say keep building the third gen stock!
For example, class 150 is a decent modern train but only two coach. Instead of tendering for brand new class years later, why not look at growth, & just build new carriages to fit spec of the original train. Then all you'd need to do is internal refurbs, repaints, maybe new engines, all done seperately down the line.
Starting with Turbo / Electrostars / Juniper / Desiro et al, let's re-open the projects (when needed). Surely it will be cheaper in the long run. 450 has a bigger brother in the 444, but no equivalent on LM WCML? I find this quite strange as there are too many places that need or would benefit from long distance E or DMUs. I think our government should support or supplement the trains & services we already have instead of dreaming up things like HS2. HS2 can come much, much later.
As for "C" I think we should be carefully selecting lines to re-open that would provide relief for congestion & link up more cities, even creating new cross country routes. I'm sure we all think Beeching went too far.