Fighter:
Levels up faster, but this is only a starting advantage. Both the Fighter and the Ranger will cap at level 30.
Deals more damage per hit
Can obtain better THAC0
Ranger:
Can potentially deal more damage per round, but at the expense of using a shield. At lower difficulties, this may be a neglible concern, but at higher difficulties, it will become a liability. I say to heck with the additional ApR and slap on a shield.
Can cast some Druidic spells.
Can Stealth, but at the expense of armour. You might as well use an Invisibility spell.
Can use some Ranger specific items.
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It may seem unlikely, but the Ranger will actually make a better tank eventually. Personal buffs from Druid spells is the key, not to mention access to special Ranger-only items.