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.