Hello, I couldn't find answer to my question anywhere; when adding an artwork to a single, what is preferable? The single artwork or the album artwork?

What do you prefer?

Because that is the one to go with.

If you have a single, then take the single cover. But there is no standard.

Did you know that it is possible to have more than one picture embedded? So you can embed both: single and album cover. (and many more for inlet, artist, booklet, back etc.)
The only problem is that hardly any player displays them in a decent fashion.

Thanks, guys. It's clear now. You really helped me.