If you have to choose one of these three mobile phones for purchase, I personally recommend that you buy the more cost-effective Xiaomi Mi 12S phone. The reasons I gave are as follows, you may wish to refer to them.
Reason 1: Among the three mobile phones, the Xiaomi Mi 12S is the lightest. The Mi 12S weighs 182 grams, while the other two phones weigh 205 grams (Mi 12 Pro) and 203.5 grams (OnePlus ACE Pro).
Reason 2: Among the three mobile phones, the Xiaomi Mi 12S is the only model that uses the Leica professional imaging system, which can be said to be remarkable in terms of photo imaging effects.
Reason 3: In addition, Xiaomi Mi 12S also uses Qualcomm Snapdragon 8 performance Audio-Technica combination, 50MP IMX707 rear main camera, 4500mAh battery, 67W wired fast charging, and Harman Kardon dual speakers, and supports NFC, infrared remote control, Wi-Fi6, and X-axis linear motors, etc., it can be said that there are all there.
Therefore, based on the above reasons, I personally recommend everyone to buy the Xiaomi Mi 12S. For the comparison of the core configuration of these three mobile phones, please refer to the following figure.