troll blood vs healing liquid

What's the difference? Is one of them more powerful, or more helpful in regenerating limbs?

Troll blood has a weaker healing effect, but has a higher satiation value effectively doubling as a food source in addition to the healing. I don't think there's any difference between the two when it comes to limb regeneration, though I could be wrong.

Shoot, I've been doing it backwards then. I always tried to save troll blood for emergencies.

If I remember aright, there's a small chance for healing liquid to regenerate multiple limbs too.

I ran a few tests through wizard mode, seems that there's actually no randomness involved to regenerating multiple limbs with healing liquid. Rather, it's based on the healing value: excess healing power goes into regenerating another limb after some certain threshold. Since troll blood has a lower healing value, you're much less likely to reach the threshold with it. Troll blood does regen two limbs as well when your endurance is low enough, i.e. when the max limb HP is very low.

When playing normally the second regenerated limb usually appears with minimal HP. When endurance falls enough, it will start appearing fully healed. The limit for regenning two fully healed arms with a healing potion is 7 END. Interestingly, since legs have more HP than arms, regenning an arm and a leg at 7 END only nets you a healthy arm and a gray leg. Same goes for two legs, one of them will pop up gray. Furthermore, seems that arms will always be preferred for the full health regen over legs.