I have experience with two livechat options.
Kayako (used daily 2006-2012)
If you use Kayako for tickets, use Kayako for livechat. It has a full feature set an integrates perfectly into your ticket system. The seamless integration is well worth it compared to any slight advantages other software may have. The multi-department tool lets you have sales or support online independently. My experience, while extended, is also from six years ago, so things may have changed.
Livechat Inc (use daily from 2012-current)
I like livechat inc, but they've failed to innovate much in the time I've used them. They're also a bit steep @ $40/seat/month. Something that keeps me loyal is the app, which is darn-near perfect for handling the tail end of a lingering livechat once you want to step away from your desk. The stats are detailed and useful. One huge negative is that they've failed to give a good way to copy and paste a chat out of the program - it comes out all scrambled. Another negative is that the reliability has dropped a little - I'd say it's sitting at about 99% whereas it used to be 100%. Their support is fast, though.
All said and done, of what I have used, I'd recommend Livechat Inc over Kayako...unless, of course, you're using Kayako for tickets. That said, if you ask me in a few years, the slow decay of my otherwise impeccable opinion of Livechat Inc may have caused my eyes to wander to another new, shiny app.