Which is the best solution for a Web Virtual Assistant based on Natural Language?
That depends on what purpose you want it for, enterprise, small business, or personal. There are quite a few companies offering customer service solutions for substantial companies. There are also a good number of qualified consultants who can implement this kind of solution for small business. And, there are do it yourself hacks available online for the hobbyist. It would also depend on what country you are in, not to mention what language your customers speak, to determine the best solution. ;^)