Kayako's interface is far less complex than Zendesk, so it looked like a good platform. Unfortunately, the features didn't work and their support team is the worst. I went back to Zendesk and I got everything to work including their chat function. Zendesk just works. You don't need support, have a lot of documentation, and have a live community.
Features might work for you, but don't expect any support from them. For them, a trial user is not handled the same as a paying user, at least that is what the sales employee said. Support keeps you waiting forever until your trial period is over.