I'm a big fan of Helpshift. Easy to install, slick UI, highly customisable.
I also really like the way you can have multiple apps supported on the one account - something that seems strangely unusual amongst their competitors.
We're huge fans of Helpshift. From the slick chat support UI to the helpful features like review request buttons, ticket assignment and tagging, we're super happy with it for Turf.ly.
Moleskine Studio