Hardened armor is just a fancy way of adding more armor to a mech. You still have to pay for every ton, plus the downsides of PSRs and speed, although taking 40 damage to force a PSR largely makes up for the -1 to said PSR.
Lamellor is just better armor. And it makes LBX weapons pretty much obselete, even more than they already were for the Clans. It also hits SRMs, and small weapons hard, plus it effectively give you a bonus to PSRs because you have to get 24 points of damage to force one. Plus you can take a 12 point hit to the head and survive.
So, in conclusion:
Lamellor + Reinforced Structure dominate.
Osteon forever!