I've used Zendesk lightly. It works well enough, but does not work for me particularly because it pops records on every call. I take non support calls too and would prefer if there was a way to make it only pop for calls that came through our support queue and not calls to my direct line, but there is not at this time. I did read that the Zendesk integration is being updated in the coming month though so maybe it will improve.
If you use it for dedicated agents it works well. Zendesk also has its own built in voice and contact center that I would consider too though.