I don't know much about Venos but from what i do know, Sage venos are more supports and Demon venos are more killers.

Sage venos have the AOE purge, which is amazing on mass pk, and perhaps a little bit more defensive stats on their skills, and Demon venos have lower cooldowns, faster channeling, higher critical chance and some control stats on their skills.

Sorry that i can't be more helpful, but i really don't know much about them.