The most beautiful place in all of the skyways? Hmm, that's a tough decision. For me, it's definitely the skyway of Marleybone. It has a haunting sort of beauty that leaves you enchanted as you sail through. After I finished Marleybone I kept wanting to go back because I missed how it looked and because I missed helping the admirals.
You just asked me a question I'll have trouble answering. XD I love the relaxing, prismatic horizon of Cool Ranch the most. The thing I've most njoy in the entire game, is climbing to the top of Elder Bluff, standing on the edge of the cliff, and yelling "I'M THE KING OF THE WORLD!" with a glass of tea and some tea cakes, just for a relaxing place with my crew. Well, Cool Ranch amazes me heavily...
I also enjoy the night of Marleybone, filled with the cornflower mists and twinkling, white stars that shine over the Windlanes and skyway. The atmosphere of it just wows me. And it you pass the Isle of Fetch, you'll see a gorgeous lighthouse, Ferris wheel, etc.
Valencia! I love it's emerald skies and green isles, also it's lightning and storms are beautiful, and its music, well, that's another thing, Marlybone comes secound, while Mooshu and Cool Ranch tie for third