You could use KeepVid, or you could use ClickToFlash, or you could use Safari's Activity window, or you could use ClipGrab, and all of these are free.
Can anyone tell me how i can download YouTube videos ideally for free.
I use both Chrome and Safari.
Did you notice that the OP uses Chrome and Safari... not Firefox?Download helper (an addon for Firefox). It does need Firefox but it can download almost any video or audio file you can find.
If you're using Safari, first try right-clicking the video to see if "Download Video" is an option. It should be if you're using the HTML5 trial.
If not, while viewing the video just click Window > Activity then identify the video in the list of elements (it will likely show something like "258K of 1.8MB" and will be the largest file on the list.
Hold the option key down and double-click the file to download.