Workstation GPU vs Consumer GPU

The workstation cards (like nVidia's Quadro cards) are meant for 3D Rendering and CAD type applications. They're optimized for very different stuff. The "consumer" cards are geared to 3D gaming applications.

If you are going to run architecture/rendering applications get a workstation GPU.

If you want to play games, watch movies, encode video, etc... just get a consumer GPU.

Now, as to which GPU to purchase once you decide... entirely depends on other factors:
1) What do you want to do/play with it?
2) What resolution is your monitor?
3) List your other system specs (CPU, RAM, Motherboard, Power Supply, etc)
4) Budget

Workstation graphics cards focus on precision, max resolution, and optimizations for rendering / CAD graphigs. Gaming graphics cards focus on speed, and trade off by providing a much lower precision than their workstation counterparts.

The hardware is very similar but the drivers are very different, the workstation ones have very specialized drivers that handle workstation applications like 3D modeling and rendering much better than their consumer equivalent, but handle games much worse than their counterpart. Whenever nVidia and AMD release new driver versions for their consumer cards, they often list the % improvements for various games, workstation cards do that for professional apps, the extra price helps offset the cost for providing specialized drivers and quick personalized support.