I always liked the idea of .32 NAA. Unfortunately, while it does offer better penetration potential then .380 due to the higher sectional density of the .312 projectile, its still really of threshold level performance due to its lack of energy. And of course, for the low recoil factor, the other problem is that most .380's are tiny and have a fair amount of recoil.
But along those lines, another promising option is .30 Luger. This is the 9x19 version of the .32 NAA.
Most 9x19 pistols can be converted to .30 Luger, making it an easy low recoil option.
.30 Luger = 85gr @ 1250fps / 295 ftlbs = Power Factor 106
While this is more then the PF 80 of .22 TCM and PF 90 of .380 it's still a good bit less recoil then the PF 145 of most standard defensive 9x19.
A 85gr .308 has a sectional density of 0.128, nearly identical to the sectional density of 0.13 for a 115gr 9mm. And at 1250fps / 295 ftlbs of energy, we would have every expectation of reliable expansion and penetration using a well designed JHP.
The only fly's in the ointment being the lack of factory defensive .30 Luger JHP and .30 luger conversion barrels.....