Best available expert system IDE

I'm an AI newbie, with only about 1 week's worth of experience
starting to read up about the subject.

But I'm the Product Manager on an enterprise software project in which
we wish to incorporate a rules-based expert system into a distributed
.NET Windows ap., and so I'm wondering...

What are the best expert system development packages that are out
there?

Are there any that integrate with Visual Studio or utilize C#?

More importantly, who offers the best integrated solution for:
creating a knowledge base (preferably using both GUI--remember we're
newbies and programming), creating an inference engine, and
incorporating that engine into our larger ap?

By the way, which is better Prolog, Lisp or something else?

I'm much less concerned at this point about things like real-time
performance than I am in finding an extremely user-friendly
development environment in which to build our prototype.

Any opinions will be greatly appreciated.

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