No, since it cuts your speed. A better nature would be something like Hasty (+speed, -def) or Naive (+speed, -sp. def). Defences are sacrificed for a mixed set.
That being said, I would suggest making Samurott purely Physical/ Special competitively.
Physical set:
- Megahorn
- Waterfall
- Aqua Jet
- Razor Shell/ Swords Dance
Special set:
- Ice Beam
- Surf/ Hydro Pump
- Grass Knot
- Aqua Jet (since it's priority STAB, just to clean up any 1HP stragglers)
Though I'm guessing this is in-game, and I have to say that it doesn't really matter what nature/ movesets you have. Samurott can have both physical and special moves and do well enough as long as its level is higher than the gyms/ E4/ Team Plasma.
