Relaxation:
 

I have been keeping records for several years now, and when I checked, this is what I came up with:
*I agree that 25 almost never will cost a player his relationship, but it will almost always cause a player with a girlfriend to a significant chunk of happiness.
*I agree that 27 will almost always raise the player's happiness a small amount. (For some reason, I have not used 26's very often.)
*However, I have become convinced that players without girlfriends do just as well set at 19 relaxation as at 22. They almost always gain a few points of happiness, and their chances of finding a girlfriend seem about the same as when set to 22 or 23.
So if you believe that happiness plays a major role in your team's success, I think the ideal relaxation settings are 27 for players with girlfriends, 19 for other players. If you think that happiness plays a less important role, then 25 and 19 probably makes more sense.