Personally I enjoy the vanilla experience of each the last three games without any mod. However I think each of them are imperfect games that can benefit from mods, and as such I use mods a majority of the time.
- Morrowind primarily benefits from mods that make game seem a bit more modern, such as MGSO. That being said, additional landmasses such as TR, and P:C are what really improve the core experience for me.
- Oblivion's early game is still fairly enjoyable, but the leveling system is absolutely atrocious. FCOM is a must.
- Skyrim has pretty good vanilla gameplay, but its strives to make all the game system too simple. This is especially evident in the menu system on PC, so the first mod I install is SkyUI.
I should note that mods such as the Unofficial Patches and the Morrowind Code Patch are so essential that I can scarcely count them as mods, rather than updates. So if those are the only mods you use, you can pretty much count yourself as vanilla players. Feel free to discuss and elaborate upon the answers you gave, or didn't, within the poll.
**Also if the next TES game didn't include modding support from Bethesda (no construction set) how would you react to that?