The best bird was this male redstart.
After getting fed up with only ever finding blue tits or great tits in nearly all nest boxes we put up, we tried to design one that redstarts might find attractive, and members of the genus paridae don't. This might be the answer -
Out of five put up in early May, two have redstart nests in them. They are set within continuous cover mature sitka, a habitat which is widespread, so we will definitely try some more next year.