Which is stronger, Pikafish or commercial paid engines?
The strongest Xiangqi engine is Pikafish.
Some claim that "paid is always stronger than free". That is wrong. First, all strong Xiangqi engines (free or paid) are adapted from Stockfish, the strongest chess engine, and Stockfish is open-source and free and is also the undisputed number one engine in chess, so this claim does not hold at all.
Note
The commercial Xiangqi engine "Xiangqi Whirlwind (象棋旋风)" illegally used Pikafish's NNUE on January 9, 2025, with conclusive evidence. After being warned, Xiangqi Whirlwind withdrew that version, but its later updates very probably "referenced" Pikafish as well (in fact, as early as 2023 it was found that Whirlwind's rules bug matched Pikafish's rules bug, so its code had already been "referenced"; see the related video).
Note
The tests use paired games from unbalanced openings. In real games, however, the draw rate is extremely high, it is extremely hard to see any strength difference, and the practical difference between strong engines is extremely slight. See What is the draw rate of top Xiangqi engines today? for details.