I'm genuinely not sure there's such a thing as the 'best' ones, because that's a seriously niche category even for Wattpad. The platform's algorithm tends to boost the most straightforward, trope-reliant romances, so the truly twisted body swap stories often sink without a trace unless you know exactly which tags to dig through. I spent a whole summer obsessed with this, sorting by 'completed' and 'body swap' and then reading the first chapter of maybe two hundred stories. Most are exactly what you'd expect: two characters hate each other, swap, learn a lesson, swap back, fall in love. The endings are telegraphed from mile away.
But the ones that stick with you are the ones that weaponize the premise. There was this one, I wish I could remember the title, where a popular girl and a bullied boy swap. The twist wasn't that they understood each other; it was that the boy, living in her body, discovered she was being systematically abused by her 'perfect' family. The story became a thriller about him using her social capital to gather evidence and expose them, while she, in his body, had to physically defend his home from his own violent father. The final swap back happened in a police station, not a prom. It was messy, morally grey, and the 'happy' ending was just survival. That kind of narrative ambition is rare there.
Another angle I've seen done well, though even fewer times, is when the swap isn't accidental but a deliberate, malicious act. A story where a person's consciousness is forcibly uploaded into another body as a form of corporate espionage or revenge. The twist ending reveals the protagonist was never the original person at all, but a copy, and the original consciousness is still trapped somewhere, setting up a horrific existential dilemma. You find these more in the sci-fi tags, buried under a mountain of 'CEO swaps with intern' stuff. The discovery process itself, wading through the generic to find that one broken, brilliant idea, is kind of the point of reading on Wattpad for me anyway.