Sorc - Orb or Spellbook

[The Secret Cow Level]

Even some types of low levels monsters already have elevated levels of MR to resist an similarly-level spellbook sorcerer:

Known monster types with elevated MR:

• Slimes
• Wriggots
• Gnarls
• Oculens
• Mugolems
• Obscuras
• Spiners
• Gorgons

Monster stats (low level)

Higher level monster of the same type have higher MR. Particularly when attacking monsters 2 levels above your character level (for optimum XP gain)

If you use a orb you might as well limited to grinding monsters 2 level below your character level, and not the ones from the aboved elevated MR list.