Depends if you want to ride fast.
For real high speed road riding the Bike Friday, Moulton (separable), Tern Verge, and Dahon Vector come to mind because they can be set up like a real road racing bike.
They are high end bikes that can do almost anything but they will be big and annoying on a bus ride.
The other folders are for more relaxed riding, but they can still cover many miles.
I think if you really got into fast/long road riding you would buy a second bike for that purpose.
For now though I think a folder is more in line with what you plan to do.
If you are going on the bus, the Brompton is at the top of the list for its small folded size.