[Forrest]

Bone lacing adds both to your body to resist damage and gives you armor.  Bone density doesn't increase your armor

[Michael Chandra]

It gives 3 reducable dice more versus 1 non-reducable die less, but it also has a higher essence cost (1.5 versus 1.2), is more expensive (30k instead of 20k), is detectable by cyberware scanners and easier detected with assensing.

[Xenon]

You need quite high armor penetration values to first reduce the normal armor to zero - and then some.
Until you do the armor bonus from Bone Lacing will not really be reduced by armor penetration.
- I'd say that is basically only an issue if you are nekkid.


A feature that comes with higher armor value is that attacks that normally deal physical damage now might deal stun instead (which often, but not always, is a bonus).



Having said that, the two augmentations are rather comparable.
...and if you want +3 armor, get a used cyber-foot