I have changed all the “and” to “&”:
Martin O’Donnell and Michael Salvatori
Martin O’Donnell & Michael Salvatori
One editor disagrees preferring the way it is typed on the front cover.
I prefer it to be in line with Musicbrainz’s join phrase equivalent.
Which should it be?
I tend to go for & unless something else is specified in the source material. Though with something like A & B and C & D, I would use “and” to join it to differentiate from the artist’s ampersand.
A further clarification of my position: When joining two artists I will use an ampersand, but for duos I will go with whatever the duo themselves favor. So we may have the duo A and B, but when joining C with D I will use C & D.
For C & D the exception would be if they used a very special joining e.g. C//D or some such.
I don’t get it why you would not follow prints for this one… 
When it’s joining in the editor I just tend to use “&”. But with duos, which are artist names, I pay attention to how they credit themselves as a duo name because an artist name affects so much more than just a joined credit.
