Flat 4/6
Nothing beats Porsche ingenuity, or the sound of a Flat motor, I can hear a Subaru or Porsche from a mile away.
I dunno other than the sound, it's a rarely used desing, but it has worked well for those who use it. It has a lower CG and Subaru says something about it going under the passenger compartment rather than through.
In a sentence, I love em' since they are just so mechanically exotic.