I use OBS with the NVEC codec - the one that is installed with the NVIDIA driver, and if you are recording anything, regardless of 3D or 2D, it is your best bet.
It's especially nice compared to normal H.264, and has the option of light compression with nominal CPU usage if you don't like large lossless files. It outputs normal MP4/H.264 files that I can then work with in Linux (as opposed to say Fraps) but uses the fact your GPU is already rendering the scene to then output it in H.264.
