Ask HN: Best password manager for teams?

I've been tasked with researching password managers for my team. I would appreciate thoughts and recommendations from fellow techies. We have over a hundred customers, each with their own various account/server/infrastructure credentials. Currently, each engineer assigned to an account stores credentials in their own password manager (1Password or LastPass, up to the individual's preference). However, we ran into a few situations where the engineer was on vacation and their customers ran into support issues, and lack of access to credentials caused delays. So we decided we need a way of storing credentials in a shared vault. We are a team of 6, but growing. We use Windows and Macs. Security and usability (in that order) are the most important factors. Price isn't a concern. Also, I'd be interested in hearing the challenges and "gotchas" people have experienced when migrating to and using these types of solutions. Thanks in advance. :)