I'll go three player before I'll go four, partialy because I don't have three arcade-o-holic friends able to come over
at the same time to play with.
I'd use ctrlr ini files so one player games (pacman etc) use the center stick, two player games use the outside sticks, and 3 & up player games use all sticks in normal order.
Not that there are many 3 player games, and many of the best 3 player games used analog inputs: trackballs, guns, or 360 degree wheels. (see partial list below) Still, three players in four player games could be played with a 3 player CP (and which three can be set with ctrlr ini files).
Some games that had at least one 3 player version (more found at
maws search)
Alien Storm
Alien vs. Predator
Armored Warriors
Battle Toads
Beast Busters
Cadillacs and Dinosaurs
The Combatribes
Crypt Killer*
Danny Sullivan's Indy Heat*
Double Dragon 3 - The Rosetta Stone
Guardians of the Hood
Hot Rod*
Ironman Stewart's Super Off-Road*
Judge Dredd
The King of Dragons
Knights of the Round
Michael Jackson's Moonwalker
Pit Fighter
Rampage
Rampage: World Tour
Rampart*
The Real Ghostbusters
Revolution X*
Segasonic the Hedgehog*
Super Sprint*
The Three Stooges In Brides Is Brides
Xenophobe
*these used analog inputs
That said, I've already done a few two player CPs. Next is probably a three player, three 360 degree wheel CP. To paraphrase another post: "Super Sprint & Offroad baby! Awe yea..."