Whatever is comfortable for the guitarists. In Flames works in the ame tuning as Nevermore, but Jesper uses a Gibson 6-string at 24.75" scale and Jeff uses a Schecter 7-string at 26.5" scale.
Despite the difference in scale Jeff (used) to use a similar gauge as Jesper simply because he dug it. But, if you were to play their individual guitars, there would be a huge difference in string tension.
It's up to the player as to what is ideal, because it's about comfort and how you play.
What's the superior flavor? Chocolate, or Strawberry?