I chose Assistly to handle our customer contact, after assessing it against ZenDesk. Both are good. I went with Assistly because I found the user experience to be better (ZenDesk defaults to updating the user on every stage of their ticket's progress) and I found Assistly themselves to be responsive (answered my questions quickly and honestly, weren't afraid to admit that they don't have features and say what is / isn't under consideration for future updates).

I'm using the Assistly knowledgebase feature too, and it is well integrated. It's a bit basic so I expect to migrate as we grow. Probably to Joomla.

Do you plan on email support only, or are you looking at social media and phone too?