Based on "buzz factor" of talk, and awareness, FPS seems would seem to me to be larger, but Gran Turismo series sales seems to make a case for driving sims being larger. 

In your assessment, which do you consider a larger genre?  I am looking this as a whole, but also the impact of Halo vs Gran Turismo in the scheme of things relating to console sales.

Really? Seriously?

FPS of course. I don't know why you would think Gran Turismo makes driving sims a larger genre. There are two FPS games that can sell comparably to it, or possibly even more. There are also far more FPS titles hanging in the multi million mark than there are racing sims. Maybe if you considered racing as a whole genre you might have a point because of Mario Kart and most Need for Speed titles.

FPS.

If you say driving games, then that is different. But driving sims... FPS wins.

FPS, but I enjoy driving games alot more..

if you include every racer, then they may be tied

The limiting thing about racing sims are, buying them up in bulk is largely unnecessary. They all strive to be the exact same game. FPS is a very broad genre, encompassing so many different playstyles, stories, settings, etc. that you could buy 10 in a year and still not get enough. Could you ever imagine buying 10 racing sims in a year? What would be the point? Think of it like sports simulations. Would you buy NBA 10, NBA Live 10 and NBA 2K10 or would you buy one and stick with it for the year? Most everyone would pick their favorite and be done with it.

FPS