I first learned the 9x4 back when Melissa Hill had her Lenormand 101 course, so that's my default. And she used to have a great online GT generator that was 9x4, and I used that a lot. And I read a lot of blogs initially by people influenced by the Treppner family, and they use this version.
I have nothing against the 8x4+4, though, and use it when I'm trying to work through a GT in the style of a teacher who uses it.