Blessings of the Loa

You can easily change your choice so no need to spend 10 minutes deciding like I did xD
The alter is right next to the NPC that give you the quest (Du'gal, /way 43, 69 in Zul'Aman).

There are 4 different Loas and starting abilities:

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• Akil'zon, Loa of Victory
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  • Blessing: Victor's Presence: 15% chance to stun your enemy for 3 sec.
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  • Blessing: Victory at Any Cost: 100% movement speed for 3 sec whenever you slay an enemy, but you also take 100% more damage from the next source. Doesn't work on players.
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• Halazzi, Loa of the Hunt
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  • Blessing: Guaranteed Yield: 15% chance to poison your enemy, dealing 5,396 Nature damage every 1 sec for 4 sec.
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  • Blessing: Predator's Gamble: 25% chance on hit to deal 100% more damage, but you also have a 25% chance on hit to deal -50% less damage.
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• Jan'alai, Loa of Fire
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  • Blessing: Ensorcelling Flame: 15% chance to Charm your enemy for 10 sec, forcing them to fight other hostile foes on your behalf.
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  • Blessing: Ravenous Glass: 100% Spell Power, but you also receive 100% more damage from all sources.
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• Nalorakk, Loa of War
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  • Blessing: War-Spoiled: 15% chance to increase Physical damage taken by 30% for 10 seconds, stacking up to 5 charges.
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  • Blessing: Reckless Feast: 25% leech, but you also take 25% more damage from all sources.
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These are only active in Zul'Aman.

There is also a common one that add "Packpeddlers" throughout Zul'Aman, I guess depending on which one you choose the NPCs will spawn on different locations. These NPCs also give you the blessings that you chose on this tree.

The alter for the quest is right next to the quest giver, it is not in the tower.

I couldn't get any of the big buffs (Akil'zon, Halazzi, Jan'alai, Nalorakk) you get while doing the campaign back at all after interacting with the altar. I was sitting with the Nalorakk buff for a few days and wanted to see if I could go back to Halazzi, but it doesn't appear possible to get anything that isn't a combination buff with a lesser loa.