For architectural work, you get really different effects using an umbrella or a softbox. The umbrellas can be used as reflectors or you can shoot through them to soften the light further. I use the Calumet umbrellas with the black cover that can be removed so you can control the amount of ambient "bounce" from the umbrella. The umbrella will "wrap" things with light because of the ambient bounce lighting from them.
Softboxes are much more directional and with care, you can make light look like its coming from windows, instead of just an overall illumination level gain like you get from umbrellas.