I recommend ActivePresenter. It’s something I use. It’s free and you can select any part of the screen and record it. You can also record an active window.
The best part: No watermarks. I just hate it when you are trying to record a professional screen cast and at the end of the video. You find out that they synced their watermark on your video. With ActivePresenter, that’s not a problem. You can record as long as you want and you have the ability to edit your videos as well.
The only down-fall for ActivePresenter is that if your video is long like 30 minutes to an hour, when you export that to .mp4 or .avi, .etc it’ll take long to convert.