Dual citizenship

Well, it is a bit hard to say because you have used both for your travels to China... Both should be fine, but since you are able to choose, I would suggest you to use Polish one and the explanation is simple. Poland as a country is listed in the Chinese 144 hour visa free transit scheme as EU country and this makes a Poland to be perceived as a member of important economic block. Also, Polish passport is ranked 5th in terms of travel freedom or better to say, it belongs in the global elite in this regard.

By the way, at the time being, only two VOAs are currently available: Shenzhen and Zhuhai VOAs. Hainan VOA is still in its trail phase and Xiamen VOA seems to be discontinued or still suspended because we have not received a single relevant feedback in this regard.