Over the years have used various 12-strings including:
Eko Ranger (yes! my first guitar)
Various Yamahas
Bozo
Fylde

All were strung with light gauge .010/.047 and all kept at concert pitch.

Current 12s are:
30+ year old Yamaha FG630
Taylor 855

Both are kept at concert pitch with light gauge .010/.047 Elixir strings, and both are occasionally played with 11th and 12th strings dropped to D.

jiva (Jimmy & Val)
www.jiva.co.uk