FNV sold more copies than F03.
Nope. In fact we have no idea which sold better because Bethesda never released the sales figures past the first week. Week one sales figures showed that they were http://news.tgn.tv/fallout-new-vegas-one-week-sales-of-1-4-million-units/, and if you're really, really determined on using NV's sales figures to support your anti-Fallout 3 argument, then I guess you can just pretend the world ended after that first week (but nobody noticed!) and that's all it sold.
Now, just because Bethesda never released official sales figures, doesn't mean we don't have unnoffical ones. But those don't help your anti-Fallout 3 argument either. VGChartz says FO3 sold http://gamrreview.vgchartz.com/game/6992/fallout-3/, while http://gamrreview.vgchartz.com/game/33663/fallout-new-vegas/. It says FO3 sold http://gamrreview.vgchartz.com/game/6993/fallout-3/, and http://gamrreview.vgchartz.com/game/33662/fallout-new-vegas/. And it says FO3 sold http://gamrreview.vgchartz.com/game/13869/fallout-3/ (more on that in a second), while http://gamrreview.vgchartz.com/game/33664/fallout-new-vegas/. And as you may have inferred by the zero copies on the PC figure, VGChartz often has innacurate sales figures and really shouldn't be taken as the truth. But, even if you did believe them, they say Fallout 3 still sold more than New Vegas, so it wouldn't help your argument.
To summarize, there's no official data out there that says New Vegas sold more copies total than Fallout 3, and even the unofficial data doesn't help your argument. As I said, the only way you can use the sales figures to your advantage is if you find a way to convince people the world ended after the first week of New Vegas' release and we're all living in some sort of matrix. You can also do what alex man142 just did and pull the answer out of thin air and hope people are too ignorant to check the facts for themselves, if you're so inclined.