As someone who would rather play Helldivers 2 and believes it's the better product, Palworld is the bigger surprise success.
Palworld has the 2nd highest CCU player count on Steam ever. Sold 25 million copies and probably around 30 million players now including Game Pass numbers. Palworld had significantly less funding and development support than Helldivers 2 as a Playstation published title. It's also the reason Helldivers 2 will have more consistent support going forward.