The favorite based on use for me would be Sanguine Rose. I don't really care for the looks of it, but I have used it to get out of many jams where I just need tank.

I have the black star with me, but I dont use enchanted weapons enough to require using it alot. I also seem to have zillions of other soul gems with me all the time, so I've never really seen it's usefulness.
I keep Dawnbreaker with me, but I always forget to use it. It has lower damage than the other (jaysus) swords I use after improving them at the smithy.

sigil stone

I think that even if your character isn't evil, you'll agree that the Black Star is more practical than the original version. That and the Skeleton Key.

In another thread, a lot of people said that the "Ebony Mail" was especially useful. Why? I would say that it's a daedric artifact, but that's it. It doesn't have that many useful effects or powers.

Spellbreaker.

@Necromancer- who is your avatar?

Thats a nice job

Wabbajack. I use it in almost every difficult boss fight - Morokei, for example.

I always wear the Ebony Mail. I like how it reacts when enemies are near.

A few characters ago, I would have said the same thing. Then my last lass got it, and decided to don it while clearing that tough bandit hideout in Pinewatch (hidden entrance in basemant).
Holy cow did that thing turn out to be "especially useful!" For enemies that like to get up close and personal, it makes a huge difference. Not only do you watch their health drain before your eyes, you barely need to exert yourself during melee.
Unfortunately I may not bother with it for my current mage in robes, but one of my followers might enjoy it.
Give it a try!

I only do quests I want the item from or like the item and keep it.

The ones I use a lot are
Spellbreaker
Dawnbreaker
Azuras Star
Saviours Hide
Hircines Ring
Ring of Namira
Sanguine Rose
Mehrunes Razor

The ones I keep are
Wabbajack. Little to no use in combat but I might see the random encounter one day.
Volundrung. Looks totally awesome.
Masque Of Clavicus Vile or The Rueful Axe. Looks good. And the axe means Barbas dies!

The rest, don't like them that much or no point getting them.

Ebony mail, good, but I don't like heavy armour.
And it looks stupid on females. Could they not stop their boobplate obbsession for chainmail?! FFS!
Since when did chainmail look anything other than flat chested!
Don't like it that much, it looks suffocating.

Ebony Mail
Sanguine Rose
Azura's Star
Ebony Blade

I used Spellbreaker extensivly in Oblivion, but have yet to use a shied in Skyrim. Perhaps on my next playthrough.
Wabbajack is fun, but it's not something I'll use for more than ten minutes.
Did Namira's quest once, but reverted to an older save. Didn't like what it made me, but it does fit the RP of my current guy, so I may do it again.
Did Mehrune's quest once, but since I betrayed him, the razor was useless to me. Planning on doing this quest without betrayal this time.

I plan on getting both Spellbreaker and Dawnbreaker on my Paladin build. I've gotten then both before, just not of the same character. I think they're both great artifacts.

Thanks. It's the best I could do with a digital camera and Photoshop. I really wish we could take proper screenshots on console games.

Never.

Black Star - For capturing souls for my enchantment
Staff of Magnus - Useful against mages and dragons
Sanguine Rose (held by Cicero) - Distraction and damage source
Chillrend (also held by Cicero) - Great weapon till I find Paralyze enchantment. After I found the enchantment I enchant another glass sword (after buffing my enchanting) and named it Chillrend Eternity.
Wabbajack - Wabbajack, Wabbajack, Wabbajack!