Below you will find a rough rankings for the various Rogue Legendaries in Legion. Each legendary is unique in it's 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

  • Greenskin's Waterlogged Wristcuffs: Currently the best legendary for Outlaw. Considerably improves single target DPS. Changes the way the spec is played.
  • Insignia of Ravenholdt: Third best legendary for ST. Best Legendary for 2+ targets.
  • Mantle of the Master Assassin: Second best ST and third best AoE legendary for Outlaw.
  • 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 legendary

Assassination

  • Duskwalker's Footpads: Unarguably Assassination's best legendary. Vendetta is incredibly powerful and this legendary combined with Vendetta relics create a huge DPS increase.
  • Mantle of the Master Assassin: On paper it looks like It's going to be a powerful legendary, however we don't know, how powerful it will be.
  • Zoldyck Family Training Shackle: Another very powerful legendary for Assassination. Not quite as good as Duskwalker's Footpads but still very strong.
  • Insignia of Ravenholdt: For 2+ targets the ring starts to overtake the above legendaries. The ring and Cindaria are about on par with each other for ST Assassination DPS increase.
  • Cinidaria, the Symbiote: Decent legendary. Nothing very noteworthy.
  • The Dreadlord's Deceit: Only useful in big AoE fights which makes it very situational.

Sublety

  • Mantle of the Master Assassin: Current testing suggests that the buff from Mantle is experienced for the duration of vanish (possibly working with subterfuge - this is still being tested). The buff from this legendary is not attainable through Shadow Dance.
  • Shadow Satyr's Walk: These were god mode in 1.0. Come 1.5, though, the energy refund is being reduced significantly. They will still offer a meaningful dps bump, but begin to fall behind bracers with tier/class trinket.
  • Denial of the Half-Giants: Bracers weren't as sought after in 1.0 as they will be in 1.5. With the tier bonuses and class trinket, Denial overtakes Satyr's Walk in dps contribution, albeit ever-so-slightly.
  • The Dreadlord's Deceit: Extremely powerful for Subtlety's AoE burst due to Shuriken Storm's interaction with stealth.
  • Insignia of Ravenholdt: A very powerful legendary despite the nerfs. Still not better than any of the other legendaries mentioned above though.
  • Cinidaria, the Symbiote: Decent legendary. Nothing very noteworthy.

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