While in regular form, there isn't a whole lot of difference between werewolves and non-werewolves, but when you transform, you get a ton of benefits and drawbacks:
Benefits
- Increased max health by 100 (non-regenerating)
- Increased max stamina by 100
- Faster sprint speed
- Wolves no longer attack you
- Committing crimes in beast form don't count against your normal form
- Immunity to all diseases, including vampirism (also cures vampirism if you have it)
- Special, werewolf-only abilities like howls
Drawbacks
- No looting (when a werewolf)
- No inventory or equipment access (when a werewolf)
- No talking (when a werewolf)
- People either run away from you, cower, or attack you (no friendly humanoid NPCs) (when a werewolf)
- If someone sees you transform, it's automatically a crime
- No rested bonus
- If caught transforming in public it's 1,000 gold bounty to pay
As far as I understand it, the only thing that matters for enchanting is the level of creature or human you soul trap. So it doesn't matter if you use a human soul or a creature soul.
However, nearly all soul gems only trap creature souls: only black soul gems will trap human souls. And black soul gems are pretty rare. Black soul gems (including the Black Star) work on humans of any level, including common NPCs like bandits. So if you're looking to expand your soul trapping opportunities, having Nelacar repair it is prudent.
However, siding with Nelacar will prevent Aranea from ever becoming a follower, which might not be what you want. While it's stated to only hold Black Souls (Humanoids) it can actually hold all types of souls, making it a straight up upgrade, as long as you're willing to go that way in the quest line.
In terms of a quest to collect all the Daedric artifacts, I'm not aware of any in game. However, if you're an achievement collector, all three platforms have:
Oblivion Walker
Collect 15 Daedric Artifacts
But both versions of the Azura's Star count for it, so choose whatever you want.
And as an aside, there is an Oghma Infinium quest, just not in the same style as Oblivion:
The reward for the quest Discerning the Transmundane is the Oghma Infinium, one of the 15 Daedric artifacts.
Best Answer
To start with, The Masque of Clavicus Vile is the true daedric artifact, and the only one of the two that counts towards the Oblivion Walker achievement. It also has one of the best benefits of any headgear for dealing with vendors.
The Rueful Axe on the other hand, is a two-handed battleaxe that may have a higher base damage than most of the weapons you can find/make depending on how early you do the quest. Unfortunately the enchantment on the axe is not particularly amazing (20 points of damage to stamina). The weapon has a speed of 0.5, which is slower than even warhammers.