Rotom Wash's Hydro Pump is the strongest.
Since accuracy doesn't really matter much in game due to availability of Potions, Hydro Pump serves as a great move. With Rotom Washes epic Special Attack, it can dent almost every Pokemon ingame. It is also useful for a lot of the Elite Four and Gym Leaders throughout the game. It also has great defencive stats to keep it good in battle. I used it to heal my Pokemon.
Hydro Pump doesn't have any Stat recoil either, making it the most reliable to use and well rounded move of them. With STAB the Base Power is 180. Good.
This is the set I used In game. I think it works really well, I hope you use it, it will be really useful throughout the game.
- Hydro Pump
- Confuse Ray
- Double Team
Yeah it's nothing for competitive, but it works like a beast in game. Just set up Double Team, then Confuse Ray the opponent and then sweep them with Discharge and Hydro Pump. It's gimmicky and you should only use this set for Gym Leaders and Elite Four's and other important trainers in game.
Rotom Wash's Stat distribution:
HP Base: 50 (210 - 304)
Attack Base: 65 (121 - 251)
Defence Base: 107 (197 - 344)
Special Attack Base: 105 (193 - 339)
Special Defence Base: 107 (197 - 344)
Speed Base: 86 (159 - 298)
Total Base Stats: 520
Hope I helped, I just really wanted to answer this because I have Rotom-W in my in game team right now. It is absolutely epic.