I think a purebred dog from a reputable breeder who only wants the betterment of the Havanese (and that is key, more so than the purity of the breed in my opinion!) allows the buyer to make a wiser, more conscious choice.
Looking at the history of that breed, the experience and history of the breeder, a buyer learns what are "acceptable" traits in the Havanese standard and if those appeal to the buyer, then they're all set.
AKC has this that might help: http://www.akc.org/future_dog_owner/...ying_a_dog.cfm
Personally, it is more important to me that I find a good breeder, who health tests and posts results for all to see, that has several years of experience, has shown, bred and is part of a network of reputable breeders/clubs/groups, socializes her puppies .... etc.... all those things we say to look for when choosing a breeder.... All that is more important to me, than actually choosing a purebred. If a breeder fits all these criteria and has been breeding Havanese x Shih Tzu, for example, for years and years, then I'm fine with that, know what I mean?
Of course, that is all moot, since the AKC and reputable clubs won't recognize that mix! O.k......... never mind!! LOL