Truly such a beautiful name, both in pronunciation and meaning. I personally think that Yuu is a more accurate transcription of the name and looks cooler, but it's up to the bearer how they want their name transcribed. A common mistake native English speakers make when pronouncing Yuu is they round out the "u" sound like in the word "you", closing their mouth on the vowel, when really you should keep your mouth in the same position the whole time. Yuu can also be a diminutive form of names that start with the same syllable like Yuki and Yuuto.