VerneMQ committer here, we haven't published any benchmarks yet. I haven't looked at the emqtt codebase in depth, but as far as I can tell they use a different clustering/distribution model than VerneMQ. I also don't know about their take on plugins.
Maybe not important for everyone, but tambur supports SSL for all pricing plans.
As pusher we are big fans of WebSockets, afaik pubnub uses some sort of long-polling for their message-handling. I am not sure if pubnub provides a way to trigger presence events. Pusher also provides these features afaik by using separate channels for e.g. presence events (not sure though). In Tambur you enable presence-events, direct- and authenticated messages on the same channel (we call them streams). So we probably have more in common with pusher than with pubnub feature-wise, we just do things a little bit differently.
Umbrella Project can be found on https://github.com/erlio/vernemq as well as our website https://verne.mq