so, here is my panel:

I saw your question about spinners and racing and everything, and it sounds like you're falling into the "one cab to do everything" routine. Don't design your panel around playing everything, design it around playing everything you like.
My design is based on NBA Jam/NFL Blitz/ NHL Open Ice, and in fact uses the CP box from an NBA Jam. I adjusted the vertical placement of the sticks to put them all on the same horizontal line. This allows me to play 2 player smash TV , Total Carnage, and Karate Champ. While not great by todays standards, I have fond memories of those games, and making them playable was literally no sacrifice, so I adjusted my design to allow those games to be played.
I also considered the 4th player buttons for the outside 2 players, but the only 2 games I can think of that use 4 buttons for those players are the 2 D&D games and then there is the 5 button Guilty Gear Isuka but I considered how rarely those would be played and how much trouble it would be to exceed 40 inputs/duplicate inputs and in the end , I thought 3 was perfect. Its all about balancing what you know you'll use and what you think you'll use.
