Y X L
B A R
I'd agree with this one, but I'm open to suggestions also as I haven't setup my SNES emulator properly yet...just thinking of making a 'this button does what' instruction card.
Edit: I mis-quoted the layout I intended before.
It depends on what you play.
If all you care about is fighters, it doesn't matter so much. But for many games L and R actually where there for left and right scroll or rotation. Eg: Contra III ("Super Probotector" for the PAL version) needed them for rotation in the overhead levels. Likewise some platformers (Super Mario World / "Mario 4") used them to scroll the screen about, and driving/flying games (Rock'n'Roll Racing, Starwing/Starfox) to add extra turn or roll to driving games.
So if they are on your list, I'd consider the...
L X R
Y B A
...approach if you absolutely *MUST* have a "6 straight" approach.
If not, something matching a SNES pad would be far more intuitive or general button use, and where the button layout was important (eg: SNES Super Smash TV).
(ASCII-art spacing not to scale):
L R
X
Y A
B
[edit note: yes, the original post had this layout mentioned]
And of course, colour match your buttons to the much cooler PAL/JAP SNES/SuperFamicom primary colours. The US SNES with it's all-purple montage was bloody ugly.
To be perfectly honest with you, I like playing SNES games on a SNES pad. I still have my original PAL SNES and Japanese Super Famicom systems plugged into the game-room's TV, ready for action at a moment's notice.
I leave sticks for arcade games and modern console fighters.