Regeneration uses bioelectric energy to heal wounds. Upgrades to this aug increase the amount of healing that occurs to a point where new limbs are grown in seconds. The energy shield provides protection from flame, energy, and plasma attacks. Regeneration is a better choice, as it will keep you healthy no matter what the source of damage. Aqualung extends your oxygen supply when swimming underwater.
Environmental resistance provides protection against radioactivity.
An upgrade to either improves their performance. Don't bother upgrading either of these augmentations, they won't see much use, and one upgrade to either aug is more than you'll ever need. A synthetic heart acts as an automatic upgrade for all of your augmentations. However, given the number of upgrade canisters available, you're better off using the power recirculator, which reduces the amount of energy used by any augmentation in use. The dream of every thief, run silent softens footsteps.