My is Oblivion the dark brotherhood quests are so much fun to me.

Don't have a favorite. 3, 4, and 5 are all amazing.

The Elder Scrolls II: Daggerfall

Also, if you haven't played it before, then try the new Unity version of Daggerfall.

My favourite would be Oblivion, but Skyrim is the most enjoyable one for me, expecially on PC (I love third person view and I hate mouse and keyboard - now I have Oblivion on PC but back then I played it on console with a gamepad).
I have played Skyrim much more because of those reasons and I have grown very fond of it. But I prefer the contents of Oblivion, expecially the setting, the side quests and the dialogues. The main quest in Oblivion was not very good but I don't care too much, there were so many fantastic sidequests and I'm more interested in those than in the main quest in a TES game.
Overall I like them both really a lot.

morrowind.. by far

honesty does oblige me to say I never mamaged to play TES II daggerfall would love to test it one day.

Morrowind. No doubt.

Skyrim

Why? Because it's the only one I've played.

They are all good in different ways

Hard to choose between Morrowind and Daggerfall.

Fallout 2

Morrowind because you get to finally purge the n'wah from our lands

Oblivion.

Never really liked Morrowind that much even when I played it back when it was still a relatively new games.

Oblivion.

It never ceases to make me laugh.

morrowind :

*better designed cities and land than any other TES game.
*no handhelding like oblivion/skyrimhave
*no unkillable npc
*no map markers but a walk by asking directions much better for immersion.
*more items, armorclasses, spells, skills, weapontypes etc..
*much more moddable NOTHING added in oblivion or skyrim was not already modded in morrowind before those 2 launched.

oblivion was severely dumbed down and skyrim even more..

at least Oblivion stopped having tourist brochure as npc.