Modular homes are only as good as the contractor that "pieces" the house together. All things being equal, modular homes do have certain advantages over stick built, namely, less or no shrinkage and settling as you may experience with a stick built home. The other consideration is that, generally speaking, modular homes are less expensive to build, certainly on a per square foot cost basis.
Having said that, if a home owner is willing to invest several million dollars in a home, it would best to interview several local builders and architects to see what they think of modular vs. stick built construction. I don't think one is necessarily better than the other, but if the home owner demands alot of "personal touches" and a significant amount of "custom work", I would definitely recommend stick built...you won't get as much customization with modular construction.
Hope this helps.
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