Well, you must have a few options you left off, but let's deal with these. It's not Castles in the Sky- that's flipping Stonemist; your odds are low. The quickest is technically WvW rank; you could buy it with laurels right now. Barring that, this is still probably the go-to as you can just go in EotM and PvE it up without a specific plan. While in EotM you can try for the 14 reactors as well (but make sure you're looking at total completion and not tier completion).
Speaking of EotM, it amazes me how little I've played there. It's so beautiful, but it feels like PvE. I really want to party with GAF next time we're the same color; perhaps y'all can show me how to EotM properly.