I don't think it's been mentioned yet, but in theory the lighter bullet should have less recoil (all else being equal).
While this may be true for many calibers, with .40 S&W most factory loads typically have similar power factors (i.e. bullet momentum), which usually means that recoil is nearly the same regardless of bullet weight. There are exceptions, such as some 135 grain loads that have the same velocity as 155 grain loads (done intentionally for reduced recoil), but the general rule is that there is not much difference.
If terminal performance is similar, the 155gr probably makes more sense.
Terminal performance is similar in this case for two reasons: 1) similar momentum in this particular caliber, and 2) Federal did a great job with their HST series (each load is a different design, really, and all are good). Some have said, however, that lighter, faster bullets tend to result in snappier recoil, while others disagree. And then there is the issue of blast & flash, which will be greater with light bullets.
Mine is loaded with 180 gr Winchster WWB jhp. If anyone says it aint a good SD defense round, well let them stand in front and i ll try a round or two.
Given the choice between getting shot by anything (down to and including a spit wad from a plastic straw) and not getting shot at all, of course I would choose to not get shot. That said, if I had to get shot by a .40 S&W bullet, then I'd rather get shot by a WWB JHP than a superior JHP that would actually work as intended. Based on the tests I've seen, you're wasting your money on these and would be just as well off using WWB FMJ (especially since in this caliber FMJ bullets all have meplats).
I go for 180 gr bec i want big and deep penetratiion and more kinetic energy dumped on the target. A 165 gr would be nice but i havent found one yet.
I agree with big and deep penetration, but lighter, faster bullets definitely have more kinetic energy.
