Short answer: knights have good damage mitigation while being able to tank with snap aggro spells. Rangers have snap aggro, but noticeably less damage mitigation due to armors with less AC and lower defense skill caps. I will leave the longer answer to a min-maxxer. I know that rangers are good to fill in group role gaps caused by missing a more role-focused class =)
__________________
[Beguiler] Vermicelli (Gnome)
|