Ask HN: What is the best method for handling a large number of domains?

Working in an agency type environment where grabbing domains for clients tends to happen quite frequently. We've been holding our domains with one registrar for the sake of simplicity and I'm starting see this more as a single point of failure rather then something convenient. I'm curious if there is a consensus regarding holding a large number of domains - is it better to split them up amongst many accounts? or is having the single account fine as long as security is maintained properly? Thanks