Mine is Lifting the Vale- given by the Countess of Bruma. I like this quest so much because it gives you access to an otherwise non-existent place. I also think the journal is very well written. I like how you have to find your own way without a quest marker.

You?

I like the Aleswell quest, because you get a free place to sleep and put stuff.

This should be in the spoilers section but oh well

I personally like Shadows over Hackdirt - because of the creepy feelings that go on there.

Also the actual Main Quest ending is nice, personally I just love the ending cinematic. Brings tears to my eyes when I think about the history between after the Main Quest and Skyrim. Somebody died for nothing it seems .

I love Paranoia, such a fun quest.

Sheogorath's shrine quest. 'Nuff said.

Oh, my character still has guilty nightmares about what she did during that quest. Those poor feline souls. :confused:

Now, Sanguine's quest. . . that still causes fond giggles and is likely our fave. :thumbsup:

I love the daedric shrine quests where we play nasty tricks on others

There are so many so I'll just name a few rather than pick one:
Meridias Shrine
Order of Virtuous Blood
Caught in the Hunt
Lifting the Vale
A Brotherhood Betrayed
Boethias Shrine
Azuras Shrine

I like The Collector series of quests from Umbacano.
I clear every mine & ruin along the way to each location.
A good way to gain experience, and open up the map.
http://www.uesp.net/wiki/Oblivion:The_Collector

I second with the OP:s favorite. Lothran and I really bonded on that quest

Well, since you said "non-guild quest" instead of "side quest," I have to go with the main quest of Shivering Isles.