Geforce series = designed with gaming/consumer use in mind
Quadro series = designed with graphics/CAD/3D/etc work stuff in mind. So much so that there are usually Nvidia released "tweaked" drivers for different things (like Autocad specific). Historically, these cards have not been very good for gaming, but are great for CAD.
Over the last couple years, the line has become a little more blurred. While the names (and some tech) still separate the 2, the Geforce series (thanks a lot to driver advancements) actually do pretty well in CAD.
So the answer, (to me) is:
If it is strictly a workstation for CAD/Graphic design, etc - Quadro still wins.
If it is a gaming/personal machine, Geforce wins.
If you want a balance of the 2, Geforce wins.