I am skeptical of rail transit in all but the largest cities since busses can do the job much more cost effectively. They also respond to increases or decreases in demand much more quickly. With hybrid busses and even electric ones, I think they make the best solution for most cities up to the large metro areas.
Interregional high speed rail makes sense. They are precisely what carries water for local and slower regional mass transit since they tend to be profitable even when taking capital costs into account.
It's a trade-off, rail in large cities is more expensive and requires additional land corridors or excavation - but buses are large, awkward and do take up room on the roads.
I generally prefer rail, light-rail or BRT (bus rapid transit) to ordinary buses.
I think inter-regional lines make the most sense.
