With there being 3 types ( hand, finger, arm), I find the hand vibrato the least restricting, more accurate in pitch, and more pleasing to the ear. I am currently working on how to teach vibrato, because it came naturally and is one of my strong suits as a violinist, it is very difficult for me to teach. I do know that sometimes it helps to hold the shoulder with each finger while your hand waves at you. It also helps to slide up and down the fingerboard with the various fingers and gradually making the motion smaller to the point where the actual flesh touching the board is not moving but your hand/fingers is/are. Either way, the vibrato is kind of the soul you can inject to music that is purely you, so have fun with it and find your voice!