At first, I'm using the keepvid.com. Easy and do not need to install. but after several times I'm using it, there was some problem.

So, now I'm using http://youtubeinmp4.com plus I'm using IDM. For me, this easy. Just dl from the youtubeinmp4.com and it will dl through the IDM. But the IDM sometimes have problem download video such as the button dl do not appear. Hehehe, this is my way to dl vid from you.