Youtube is the most popular and every one definetly visit at least one per day either for entertainment purpose or to learn something.every songs every video every great clips and every thing from project to lab techniques we can learn by watching video on youtube.
Best thing is that on this site so many video quality options are there so even if your net is very slow you can atleast able to see it may be not in hd but at least you can see it.now youtube comes up with new feature known as youtube offline where you can save the video in high quality to watch it later.if you have skill you can add your own video and can make money from it.now a days live streaming is also gradually increasing on youtube.
This is best site powered by google and very easy to use and greatly design plus while watching video they show us related videos which is also nice.overall it is the best and now its not posible to sped day without it