It's a tie between -xx- and x--x.
There is a similarity between the the center types, in that they both direction represent your functions.
The book-end types are attitude and preference, so they sort of share the fact that they both determine function management, in a sense.
It's like -xx- represents the dynamo of your mind, and x--x represents the gyro.
I think these are the best two in conjunction with each other.