I'm in.
I have a hard time giving it to either Xenoblade Chronicles or Prince of Persia: The Sands of Time. Giving it to either feels like a betrayal of the other. Not to mention, they are very hard to compare. But, as of right now, I have been favoring The Sands of Time. It may not have the better world, but it does require fewer mundane tasks, felt way less heavy-handed in its storytelling, and had far better gameplay.
With that said, The Sands of Time was simply one of the most fun games I've played. It had simple platforming mechanics, but it put what it did have to great use and absolutely nailed the pure joy of navigating the levels. Climbing the Tower of Dawn at the end is still the most memorable experience I've ever had in a game. The puzzles were all very enjoyable to try figuring out, and the combat, though not as good as in Warrior Within or The Two Thrones, was very exciting, albeit a little repetitive at times.
The game also had some very good writing, even if it was simple. The storybook style of writing really gave the game a charm few others have. The Prince and Farah are two of the best characters I've seen in any game, and the same can be said of the relationship that developed between them. The game also never lost sight of the fact that it was a game. They minimized the non-interactive parts as much as possible and used the gameplay and the comments made during the gameplay to really help build the characters and relationship without making the player sit through hours' worth of cutscenes. I know plenty of games have done that, but I haven't seen it done in other games as well as The Sands of Time did it.
There are other things that I love about it, such as how the art style has made the game look appealing even after ten years and as the graphical fidelity falls further behind. However, I'd say that the near unmatched gameplay combined with one of the most enjoyable stories, and certainly the best romance story, I've seen in a game is what really sets it apart from other games.