Well, in many moveset questions I've seen:
-(eg.)Fire blast/flamethrower-Power or accuracy
So which should I prefer? With high power I can OHKO other pokemons fastly but if it misses my plans will fall... So power or accuracy? Ice beam or blizzard? Thunder or thunderbolt? Surf or hydro pump?
It depends on Pokémon's role. For sweeper, power and accuracy are neccesary. Wall with Toxic may risk missing.
BTW, some may be joined together, like Thunder while raining, Blizzard while hailstorm, anything with Lock On/No Guard/Mind Reader