Purely for looks I would have to say the Cosmodrome. All of the old buildings, the posters on the wall in cyrillic, the old colony ships towering up into the sky, the abandoned aircraft in the Mothyards, the wrecked ships and shipyards in the Forgotten Shores. It all comes together to paint a very post-apocalyptic feel that has a bit of nostalgia s well. For play value I have to say my favorite place is the Ember Caves, the entrance to the House of Winter. There are a ton of Fallen that spawn here along with a Major Level at the top. They respawn really fast so you can actually run through and clear the enemies, the caves, and material nodes and by the time you loop back around they will have all respawned. Its a prime place to farm up for some items and also if you need a bunch of cash you can pop an Ether Seed and rake in the Glimmer (I bought a bunch of Rare Fusion Rifles for future proofing on another character, set me back like 16k).