expo = 博览会 world expo = 世博会

chinese exhibition hall .EXPO means世博会。you are right.(在expo那儿个国家追好看？)we dont use 追。we use 最。最好看！

well I've just been to expo half months ago. I think Italian ,Swiss and Oil pavilion is good.Though China pavilion is amazing,you should get the reserve,and it's really hard to get.

就问题本身来回答的话：到世博园区，你看到哪个场馆的队排的最长，哪个就最好看？咯咯

Well, it's really hard to tell which pavilion is the most beautiful. Every pavilion has it's own feature. And besides there are toooo many pavilions and one person can't visit all of them. =)