Tubemate is one of the powerful youtube downloader which can download videos on all the resolution uploaded by the user I am using this app since 2 years the app is very small in size.
And works very smooth and no login or registration required it saves the video in the sd card you can download videos from the others site the downloading speed is very fast and there is no stopping or pausing during downloading which good some of the downloaders stop unfortunately but it doesnt you can download music too the loading time is very less and the app is well optimised