For stock you always want the strongest rotor, thats how you make power with limited turns. In mod you run softer or different rotors to change how they drive and to make low turn motors in 2ws easier to drive.

So get the strongest rotor, you dont need the highest end works motor if its not in the budget, the stronger rotor is more important. Filling out what you'll mainly be using the motor for on their website will help them set the timing and such to what you need so you don't have to worry about that.