Comparing Music folders on 2 different hard drives

I just discovered that my wife has music on her hard drive that I don’t have and vice versa. I think it all involves music from physical CDs we’ve each purchased and ripped. This has apparently been going on for several years. Being a belt and suspenders guy I’m thinking I’ll clone our external music drives and either merge to one of them or to a third drive. The question now becomes what do y’all think is the best software for the task and what gotchas do you see?