Roserade: Grass or Poison set?
Note: IVs are A/D/S. Mons are level 30 unless stated otherwise.
I used a Sinnoh Stone on a level 15 Roselia (13/15/15). The Roserade got Razor Leaf and Sludge Bomb.
Of course, the Grass set has immediate relevance against the current legendaries, but since Roserade is weak to Blizzard and I have no Poison attackers, would the Poison set be a better investment in the long run?
Dust: 1.68M
FTMs: 44
CTMs: 25
RC: 323 (parked 250 with Mewtwo)
Water team:
Gyarados, WF/HP, 15/14/15 (maxed)
Kyogre, WF/HP, 13/13/14
Gyarados, WF/HP, 14/15/13
Gyarados, WF/HP, 15/10/14
Feraligatr, WF/HC, 14/14/15
Vaporeon, WG/HP, 15/14/14
Grass team:
Venusaur, RL/FP, 14/15/9
Sceptile, BS/LB, 12/12/15
K-Exeggutor, BS/So, 13/14/10
Venusaur, RL/So, 15/15/15
Venusaur, VW/So, 11/14/15
Electric team:
Raikou, TS/WC, 14/10/15
Electivire, TS/WC, 14/15/14
Steel team:
Metagross, BP/MM, 15/15/15 (maxed)
Metagross, BP/MM, 14/14/15
Metagross, BP/MM, 15/12/15
Other potential additions to the above teams:
Gyarados, Bi/Cr, 14/13/12, already level 30 (use TMs to get WF/HP)
A-Exeggutor, BS/So, 15/15/14, currently level 14
Venusaur, VW/FP, 15/15/14, currently level 15
Mewtwo, PC/IB, 15/15/15, currently level 20 (unlock 2CM, get TB)
Jolteon, TS/TB, 12/12/13, currently level 27
Jolteon, TS/TB, 15/12/13, currently level 11
Metagross, BP/MM, 11/14/14, currently level 20
Metagross, ZH/MM, 12/12/15, currently level 20 (use FTM)
Metagross, ZH/MM, 11/15/13, currently level 20 (use FTM)
Unfortunately, I am short on Electabuzz candy (despite having another 96%).
Answers
Poison isn't really an important PvE type and it doesn't seem like you need more attackers against the current legendaries. I don't think I would invest any resources into the Roserade at the moment, just bank it to wait for future.
Blizzard Kyogre is the only thing against which you don't currently have a good team of six and Roserade would not help you there.