Is it true Imperial Shih tzu are better than the Standard Variety?

No. There is no 'imperial' or 'standard'. A shih tzu is a shih tzu.
References :

Imperial !! Hay a new sales gimmick, I never thaught of that one before. ROFL
References :
breeder trainer exhibitor

there rwally is no difference. an imperial shih tzu doesnt mean anything whats so ever!
References :

According to the American Shih Tzu Club, the term Imperial is used for undersized dogs (runts of the litter). My Shih Tzu was the runt of the litter and she is terrific, but of course I'm very biased. It really shouldn't matter if you get a runt or a standard sized dog as long as it is health and of sound temperament. Hope the web site helps you.

http://www.shihtzu.org/Info/imperial.asp?menu=Info
References :

Imperial and Standard Shih Tzu are just two different sized Shih Tzu. Imperial is a name for the under 9 pound Shih Tzu. The imperial is better for all the people like myself, who like smaller sized dogs. The AKC says a standard is 9-16 pounds. Thats a little big for a lap dog. I wonder where the ones over 16 pounds fit in. I've seen lots of them that are way over 16 pounds.
References :
http://www.rompinlilshihtzu.com/historyinfo.html
http://www.imperialshihtzu.org/
http://www.cidclub.com/breed_standard.htm

Imperial is a term used by many breeders to represent smaller then standard dogs. Often times these dogs are ill and have life long health problems from being bred down so small. The AKC standard is in place and states that Shih Tzu's should be 9-16lbs at maturity. There is many reasons AKC has yet to allow so called Imperials in the ring (although they can be registered as a Shih Tzu because in face thats all they are). Breeders take advantage of the small dog craze right now and charge much more for these undersized dogs then a standard sized Shih Tzu. I have seen some for upwards of $3000, which is insane for a non show quality dog. If you want a healthy, long living pet get a standard sized. Save your money, vet bills and heartache!
References :