OTR has issues in instant messaging (if the messages arrive out-of-order you have to restart the session). Also, OTR's security is session based while Axolotl's

OTR has issues in instant messaging (if the messages arrive out-of-order you have to restart the session). Also, OTR's security is session based while Axolotl's is message based (Axolotl is an improvement on OTR that Signal uses).