Since Capcom fighters are among the more popular on SRK, most people will tell you to go:
 /\ R1 L1
X O R2 L2
which is the configuration on the HRAP2, HRAP3, and Mad Catz SFIV FightSticks. However, in all honesty, it really depends on what the actual shape of your button layout is.
Are you using an American 8 button 4x2 straight layout? Are you using a Japanese 8 button 4x2 curved layout? And if it’s the latter, are you using a HRAP1 curve? A HRAP2 or HRAP3 curve? Maybe even the Vewlix curve on the Mad Catz FightSticks? Really, that’s the key issue here. We can give you a much better opinion if you can tell us exactly what kind of panel button layout you have.