To be honest, I don't think either should auto-play anyway. I personally prefer to using the Youtube website on my phone vs the app because its a better experience. Given that situation, I am usually looking for the video description and/or comments rather than the video before I start watching it. Unfortunately, Youtube hides the description under a tap icon and you have to scroll past all of the recommended videos to see the comments. Its not an ideal experience.
For starter you could restrict the autoplay the next video only if it is the same element.
Handle playlists as a stream instead of multiple videos. Then you only have to hit play to start the stream.