I've been using Shadowplay ever since it got released. Before shadowplay was a thing I was swapping between Fraps and Dxtory, Fraps for lossless RGB and high framerate footage and dxtory for just ordinary gameplay. Both had a pretty big performance hit and when I tried out shadowplay it was like night and day. Barely no performance hit at all, at a high bitrate (basically lossless if you increase it to almost maximum) and high framerate, with low size output files.
There's a few features missing from Shadowplay though, mainly from Dxtory which has a lot of different settings for audio. You were able to create multiple audio sources in Dxtory making it easy to distinguish and edit in-game sound, your microphone and Teamspeak/mumble, all separetely.
http://i.imgur.com/oeAQtJAm.png
This is probably the most wanted feature right now for Shadowplay and would make it the go to recording software (which it essentially already is).
Thanks.