Which free software is recommended to record gameplay video's

http://www.razerzone.com/ca-en/cortex/game-booster

make sure you are getting it for the capture, not the booster part :)

I have used many ones like FRAPS, Bandicam and Camtasia. As for FRAPS, the output size is too big which severely slow down my system speed and meanwhile there is a dramatic fps loss in the course of recording as you can see from complaints(https://www.google.com/search?q=fraps+fps+drop&oq=fraps+fps+drop&aqs=chrome.0.69i59l2j69i61j0l2j69i60.4048j0j7&sourceid=chrome&ie=UTF-8.) Camtasia has a better fps output but the most disgusting is its CAMREC file which is the recording file, every time you must manually convert it to regular formats like MP4 and AVI, you can see how complicated the process is : http://www.videoconverterfactory.com/tips/camrec-to-avi.html
The best is Bandicam, although it is inevitable to avoid fps drop during the recording, but i think bandicam has done far better than his two counterparts