The official one.
I happen to be lucky enough to live near the only Xiaomi store in my country and I tried the 50w charging pad with my 13U but it doesn't do the full 50w no matter what because the camera bump is too big and it only does 30w if I get it in just the right position, same issue with the 30w wireless charger only doing normal wireless charging speeds.
Just use a normal wireless charger.