It's a matter of taste. 7ths work in some kinds of tunes and not in others; they hardly ever work in British or Irish traditional music, for example, though a lot of people who don't perhaps understand the idiom do seem to insist on using them. They tend to screw up the tune. So far as traditional music is concerned, the golden rule is never to use a note in an accompaniment that doesn't occur in the melody you are accompanying; unless you really know what you're doing.