Screen video capture software need some tricks if you want to record in the highest quality:

• For the best quality it is record video from screen using HUFFYUV lossless codec. Huffyuv provides very good quality, but generates a data stream of 10-15 MB/sec.
  
  If your hard drive is not fast enough then you may use a MOTION JPEG codec: Morgan MJPEG, PICVideo MJPEG, MainConcept MJPEG. Motion JPEG codecs generate data stream of 3-8 MB/sec while providing good quality.
• If you need MPEG-4 or MPEG-4 AVC video, recompress your recording using CRF (quality based) 1-pass encoding. You can use free x264 for creating MPEG-4 AVC videos and free XVid for MPEG-4 videos. I recommend you to use MKV or MP4 container for your files depending on hardware that you have.
• When you record anything from screen, close all unnecessary applications including instant messengers, e-mail clients, Web-browsers. It is also a good idea to stop your antivirus, anti-malware, anti-spyware software, disconnect from the Internet (if your game doesn't require it) and stop your firewall.
  Don't forget to turn on your system protection after recording.
  
• Consider lowering the desktop screen resolution
  
• You may need to turn off hardware acceleration when recording from screen. Otherwise you may get black screen instead of the video.

p.s. Personally I don't use MOTION JPEG or HUFFYUV. I prefer to use MPEG-2 video codec instead. It gives good quality while producing smaller files.