While Janus is a great platform to manage the agents, OpenSIPS is be a great choice for call queuing and distribution. So why not combining them to get the best possible solution? The agents will take full advantage of a WebRTC system - it is flexible and easy to use by the agents and also more flexible for the operator when comes to integration. On the other hand, an OpenSIPS Call Center manager is able to host large amounts of queues and agents (and their skills), to queue thousand of calls and to distribute a high CPS to agents, using complex algorithms. But the most important aspects is the ability of such engine to scale as capacity, but also to be geo-distributed.
