Then why do so many people use 7 for Neo Geo?
Sorry...I can be dumb
I thought we already covered this, but here goes again:
Neo-Geo only used 4 buttons (per player) at most. They were layed out kind of like this:
2 3 4
1
It was really more of a curved line, but that's the best I can do with plain text.
No one actually uses 7 buttons for Neo-Geo. But what people do is they use 6 buttons for Street Fighter II and similar games. This makes two rows of three buttons each:
1 2 3
4 5 6
Then they add a fourth button to one of the rows (or slightly higher or lower) which forms a Neo-Geo style layout on the bottom row:
1 2 3
4 5 6
7
The seventh button is redundant -- it is only there so that the position of the buttons on the lower row form the same "shape" that it does on a Neo-Geo cabinet.
What has been discussed here is how to map those seven buttons (if you chose this layout), and whether or not the layout is even useful at all. I personally don't believe it is (and I've had a machine with this layout for a year and a half now). It's only real advantage is that the buttons end up lining up with the on-screen instructions that some of the Neo-Geo games provide (watch the demo of Metal Slug, or most of the fighter games, and you'll see what I mean). How important that is to you is a personal choice.
-Jeff