Next best is ....
My little Karl Bub Sonderklasse locomotive ... its a OO/HO fellow , built in 1938 ( and yes good old Adolph messed it up for everyone , and as such it was only made that one part year )
Bing and others had already "invented" OO locomotives a decade before , but this little Bub took things to a whole new level ... It is indeed still clockwork , but the intricate mechanism allowed you to quickly set 5 different speeds with the aid of a little spanner!
And yes thats the original paperwork and spanner!
Only 13 cm long ( 5 inches) so much goodness in such a teeny package 
This is one of the locos where I truly don't know how rare it is , I suspect due to timing not too many where made , and as to how many survived , well its the only one I have seen for sale, ever .. I was lucky enough to have grabbed it .
