Recommended mapping for arcade cabinet controls to work with multiple emulators

[juan9999]

I've just installed retroarch and intend on installing as many classic emulators on my arcade cabinet as possible.

Is there a recommended setting or mapping for a two player arcade config (2 player, 2 rows of 3 button each, with 3 controls on each player (start, select, ...) that will work with the most emulators/games possible?

Something like:

X Y L1

B A R1

with controls start, select, quit (quit is not a player mapping but rather a retroarch control mapping to exit to front end)

What are your recommendations and why?

[Drnick]

This one is a personal preference jobby,  I wanted to map them to be as close to original layout as possible so ended up with this setup for consoles. As soon as you throw shoulder buttons (Snes)  or 4 in a row (NeoGeo) requirements you have to make allowances.  I have a slightly curved layout so its a bit more forgiving.   

Nes = BAStart BASelect
Sega MS = 121 121 (1 acts as start on MS)
Snes = LRY XBA OR LYX BAR
Genesis = XYZ ABC
NeoGeo = 123 444

[juan9999]

Do you use retroarch?  If so how do you pass it the config (specific for each emulator)