Tests are differ :)
I prefer undamaged stamps on paper than crumpled stamps without corners.
Milan, in China there are over 30 millions of stamp collectors, they prefere to collect chinese stamps, so it is very difficult to find modern chinese cancelled stamps.
In the previous swap from China (http://100stamps.club/stamps/CN-407) there were 2 chinese stamps, one of them was damaged.
Yesterday, for example, I received a letter from Turks and Caicos Islands (http://100stamps.club/stamps/TC-71) with 100 stamps of Canada :O)