silver umbrellas get my vote, and i find them to be much more versatile than sofboxes. but that's just personal taste.
you can go from:
to:
to:
all shot with one umbrella.
modeling light bulbs just help you see where the light is falling. if you are using softboxes with the baffles, or using a lot of grids, then you would need a brighter bulb so you can see a bit better, as these modifiers will cut your modeling light down significantly.