Tube mate is one of the best applications right now. It is not in Google play store but you can download one of the best authorized sources it’s not containing any viruses and malware its safe for you phone. You can use this to watch YouTube videos online as well as offline because using this application you can easily download the high quality as well as low quality videos in your smart phone.
As per my experience it is better thane currently available YouTube downloader applications in Google play store. I will definitely recommend you to download this application in you Smartphone.