Here's some suggestions for you -
Level 2 - Keep on the Borderlands Level 2 Ghost Great Axe
Level 4-9 Carnifex or if a less farming alternative Hellstroke Axe
Level 7 - Twinchopper
Level 10 - 19 Sword of Shadows if unbale to attain Borovian Great Axe
Level 20 The Keep on the Borderlands Level 20 Ghostly or Silver Great Axe (or just stick with the above choices, or upgrade SOS)
Level 21 - Drow Greataxe of the Weapon Master (or use upgraded SOS until 29/gotten raid axe/great sword)
Level 29 - Legendary Borovian Great Axe
Raid Axe Depends on Gearing of Character - Baz'Morath, the Curator of Decay, The Magmatic Cleaver or
Attuned Bone Greataxe are fun choices for end game.