Personally I would go with strait up Darwin with Apache (free, and for a website, that's all you really need... 10.2 has no real advantages for a webserver)... but between the two, 10.2 server hands down.
Not like WebStar is a bad product, but it's proprietary. Why go down that road? Unless you need something it offers. I just don't see why you would want to spend the money.