Below you will find rough rankings for the various dps-specific rogue legendaries in Legion. Each legendary is unique in its situational DPS increase but a few clearly stand out from the rest. More details and legendary specific guides will be written in the future.

Outlaw

  • Mantle of the Master Assassin: Best legendary for ST and third best AoE legendary for Outlaw. TB becomes significantly more valuable when you acquire these as the more vanishes you can fit into an encounter, the better.

  • Greenskin's Waterlogged Wristcuffs: In 1.5, these were nerfed from a 400% increase to 200%. Those changes and the advent of Mantle of the Master Assassin knocked the bracers out of the top spot. They are currently simming as second only to Mantle - sims.

  • Insignia of Ravenholdt: Third best legendary for ST. Best Legendary for 2+ targets.

  • Thraxi's Tricksy Treads: The value of this legendary is much lower than the above three. It still brings a decent damage increase but it forces you to change the way the class is played. To optimize this legendary you will need to use sprint as a DPS cooldown and take the Hit and Run talent. This effectively removes almost all of the mobility of the class.

  • Shivarran Symmetry: Worthless in ST. Above two targets the value is increased. Useful for mythic+ dungeons and fights with a lot of adds.

  • Cinidaria, the Symbiote: Outlaw's weakest ST legendary. This legendary does, however, perform very well on Grand Magistrix.

Assassination

  • Duskwalker's Footpads: Incredibly powerful legendary for Assassination. Stacking Master Assassin relics in combination with these boots makes for a more-than-significant dps increase.

  • Mantle of the Master Assassin: Possibly BiS in combination with DoS. Your opener changes with these equipped - reference. Subterfuge becomes a viable talent upon acquiring this legendary.

  • Zoldyck Family Training Shackle: Another very powerful legendary for Assassination. Performs well during farm and progress. These are strong in progress due to the dps increase during "execute" phase (sub 30%). Tip: Save your last vanish for "execute" phase.

  • Insignia of Ravenholdt: 2+ targets, the ring starts to overtake the above legendaries. Insig and Cinidaria are on par with each other for ST Assassination DPS increase.

  • Cinidaria, the Symbiote: Cinidaria performs extremely well on Grand Magistrix.

  • The Dreadlord's Deceit: Only useful in big AoE fights which makes it very situational. Great stat stick.

Subtlety

  • Shadow Satyr's Walk: These were god mode in 1.0. Come 1.5, though, the energy refund is being reduced significantly. They still provide the best dps bump for the spec, but begin to fall behind bracers with tier.

  • Mantle of the Master Assassin: Current testing shows that you maintain Mantle's buff through the duration of Subterfuge. The buff from this legendary is not attainable through Shadow Dance. Your opener will change slightly once you acquire these and you'll want to become proficient with your Sprint CD.

  • Denial of the Half-Giants: Bracers weren't as sought after in 1.0 as they will be in 1.5. With the tier bonus, Denial overtakes Satyr's Walk in dps contribution, albeit ever-so-slightly.

  • Insignia of Ravenholdt: A very powerful legendary despite the nerfs.

  • The Dreadlord's Deceit: Extremely powerful for Subtlety's AoE burst due to Shuriken Storm's interaction with stealth.

  • Cinidaria, the Symbiote: Cinidaria performs extremely well on Grand Magistrix.

More detailed information and math can be found on Aethys' Spreadsheet: https://goo.gl/VSjNfw?