I'd choose copy-paste for the whole process of copying/cutting and pasting text around, because that's one everybody (both beginners and advanced users) would understand. Tags shouldn't trigger questions.
Another reason is that it could happen that kill
and yank
are not the only way, or not the more natural, to achieve the wanted action (for example rectangle regions, CUA functions...).
kill and yank can still be used when the question specifically refers to the behavior of the corresponding function.
You didn't ask it, but I don't think we'd need a cut-paste either, this could be synonymized to copy-paste. After all, "copy" = "cut and paste twice", isn't that how everybody does that? ;)