+1 for everything that's been said. Another thing to consider is message throughput, if that's a concern. In the case of multiple channels per single connection, note that a connection is a single TCP connection such that multiple channels contend for the TCP stream. At the same time, connections aren't completely free either.
The general takeaway from this should be: if you've got a particular stream of messages (either a producer or a consumer) that pushes many thousands or even tens of thousands of messages per second, use a separate TCP connection. For anything else that is slower (dozens of messages per second), multiple channels on the same connection work great.
One last consideration is that when a given channel misbehaves or you perform an operation that the broker doesn't like, the only recovery that I've seen is to shut down the entire connection which can affect others channels on the same connection.
The general takeaway from this should be: if you've got a particular stream of messages (either a producer or a consumer) that pushes many thousands or even tens of thousands of messages per second, use a separate TCP connection. For anything else that is slower (dozens of messages per second), multiple channels on the same connection work great.
One last consideration is that when a given channel misbehaves or you perform an operation that the broker doesn't like, the only recovery that I've seen is to shut down the entire connection which can affect others channels on the same connection.