For my part I think it is "Frostflow Abyss". Finding a lightouse you get the chance to investigate and find out what happened and the quest in itself isn't really hard or anything. It's just amazingly well made and ties the stories and diaries perfectly together with what you find. Also the end of the quest is a bit of a puzzle where the solution wasn't 100% obvious until I did some more thinking and investigation.

So which quest do you consider to be the best in your skyrim experience?

I think Frostflow Abyss is a good candidate. Personally I like some of the "city-quests" the best. like the Potema-quest in Solitude and "Blood on the ice", but I think my favourite has to be "Laid to rest", I loved the atmosphere in that one.

Why is just a matter of personal taste i guess, but I do have a certain week spot for quests that involve some kind of creepy mystery, like all the mentioned quests so far..

Hmm, the first quest that came to my mind was the Loud and Clear quest in the Thieves Guild. Quite like that one, wish there were more similiar quests in the game

Ah yes, Laid to rest is a good one, it did have this creepy feeling over it. The way the citizens talked about it and the way the people involved seem to care so little made me question what the heck had happened here. Blood on Ice was also one of those quests that managed to grab you and make you interested in trying to figure out what had happened. The Potema quest was at first something I thought would be this small simple quest, although it turned out to be something quite different. I love how these quests all had something that just made me question "what is going on?" rather then just go ahead do the quest and deliver it.