"Best" is a highly subjective term and is the topic of endless debate.
124gr ammo tends to perform better when fired through tough barriers such as auto glass, but it's dubious whether this is beneficial for civilian SD ammo, since the goal in most civilian SD scenarios is to escape and/or stop the attack rather than to take down a determined BG who is barricaded behind cover.
Recoil can be a factor. I find that 115gr loads tend to be more "snappy" while 124gr-147gr loads tend to be more "pushy".
There are excellent SD loadings available in both bullet weights. Pick the one that works for YOU and is accurate in YOUR gun.
"Smokey, this is not 'Nam. This is bowling. There are rules... MARK IT ZERO!!" - Walter Sobchak