A) It depends on the market you are selling into. I think for people >35 or non-tech people, the knowledge of live chat isn't there. We have found in our sales efforts that offering people 1. An email we monitor regularly and 2. A phone number that reaches a competent person, is best. It is pretty much 50/50 how people reach out, what matters more is how quickly you clue in to their actual problem.
B) Our market is not tech-savvy and requires us to communicate using more typical business communication methods such as email and phone (as opposed to live chat). We tried live chat, and no one ever used it. It was more overhead to support (be online, etc.) than it gained us. The answer lies in who you sell to.