All of the chat services integrate through simple JavaScript snippets, so you can use any of them. Their prices and feature sets vary widely.

We're currently using ProvideSupport.com as our support chat. It is reasonably good and inexpensive.

We've used LivePerson.net in the past, and while it is much more feature-rich, particularly for managers of chat agents, we found the pricing to be unreasonably high and the support slow.

We're currently exploring LiveChatInc.com.

We've heard some good things about BoldChat.

Bottom line, this choice has nothing to do with Webvanta -- you need to choose the service with the features you want at a price you can afford, and the array of options is complex.