For architectural work, I would definitely go with Viz over LightWave. Lightwave has NO architectural tools whatsoever, no stairs, no moulding presets, no doors, no windows. You have to build your walls in pieces, or boolean out holes for doors and windows. Alignments are not precise. It doesn't support .dwg or any CAD imports (although there is a new $200 simple CAD plug-in you can buy for the soon-to-be-released version 9). After building several houses as props for one of my clients this past winter, I can tell you for sure that architectural work in LW is FAR too time-consuming and imprecise.
Viz interfaces well with AutoCAD and 3dsMax because they are all Autodesk products, and knowledge of Viz is likely to make you more employable in your chosen field. Many architects use Autodesk products; only a few use LightWave. I am buying Max this spring primarily so I can interface with my architectural-product clients better, despite having used LW for more than 3 years and being comfortable with its toolset.
On the plus side for LightWave, the application is far less expensive, and the out-of-the-box renderer produces nicer results. I think Viz still uses the Lightscape renderer, which I--personally--don't particularly like. OTOH, if you're pursuing further education, the cost of educational SW (Viz, for example), is quite reasonable, and you can later upgrade your license to the full commercial version.
LightWave's real strengths are in organic modeling and any form of illustration not requiring exact precision. It also has good animation tools. It's a great piece of software, but not one I would recommend for someone primarily interested in architectural visualization. | 
