The grandest of all is of course the massive China Pavilion. I was lucky to get the ticket by arriving at 7:30am, 1.5hr before it opens. To be sure, they say you need to arrive at 4am or 5am to get it! There were already thousands of people queuing in front of me when I reached the Expo gates.
The Taiwan, Hong Kong and Macau pavilions are all around the China National Pavilions, and they are all rather small. The Chinese have probably made it clear that since these should not be regarded as independent countries, they cannot have pavilions larger than that of a typical souvenir state. Macau's has two rabbit ears, which they say represent the legendary rabbit of the fairy Chang-Er. I suspect more people would think it has something to do with Macau's bunny and gambling sleaziness.
I also visited the Chinese provincial pavilions...some of them are very well built...in fact better than many independent countries. Xinjiang pavilion, together with a few others, have fantastic scaled videos. BTW, the Xinjiang pavilion caries the slogan "Xinjiang is a wonderful place".