Currently they are Kamadan, Kaineng Center and Lion's Arch / Boreal Station.
Problem is in Kamadan you can only have 4 players in the party, while in Kaineng you can have 8 and LA 6. Mapping with heroes is slightly annoying, because you need to reform your party after every pivot. I realize one can always pivot via Embark Beach, but travelling directly is just faster. I don't usually pivot via Boreal Station either because I want to stop by Lion's Arch and see who's buying and selling there.
Suggestion: change pivot points Lion's Arch -> Droknar's Forge and Kamadan -> Sunspear Sanctuary (or Kodash Bazaar, or similar). You can find the Rune Traders and Material traders there too, so no harm done.
J



