DX11 has a lot less glitches in games for me - Eternal Darkness, TMNT, Mario Golf, Ghostbusters and on and on. What games work better on DX9? It's only a little bit faster but if you have a good CPU, that doesn't matter. DX11 for the win!!
Intel Core i5 2500k @ 4.3 ghz. (Sandy Bridge CPU) / Asus P8P67 / 4 Gig Ram / GeForce GTX 660/ Creative X-fi / Win 8.1 Pro 64 bit