Edit: Assume with the digitization that you gain abilities commensuerate with those in the world you are visiting; i.e. going into Norrath would grant you innate camo, sow etc and prowess with weapons.
5. Kunark. I think Field of Bone, The Overthere, Emerald Jungle, City of Mist, The Frontier Mountains (Nurga and Droga) and Dreadlands would be worth exploring. It would be much more treacherous than Velious. FV would would look neat in person.
4. Velious. Definitely I'd want to see Crystal Caverns, Siren's Grotto and Cobalt Scar. There's no reason for me to want to see Kael Drakkal, but Skyshrine would definitely be epic to see. Additionally, Thurgadin seems like good place to party.
3. Azshara. The land of eternal Autumn. Endless artifacts and ruins. The ocean which means seafood.
2. Stranglethorn Vale. The awesome city of Booty Bay. The opportunity to become a pirate. Jungle flora and fauna. Gladiatorial competition at The Arena. The tribal civilization here would be cool to study, assuming you don't get killed. And the warm weather, shorts year round and best beaches.
1. Teldrassil:
'nuff said.
edit: 2x tag failure