MY journey through Elder Scrolls :
Arena: never played
Daggerfall: it was great and lots of fond memories... but ancient past and I'd never start it up again
Redguard: never played
Battlespire: BOOBS! ...khm... it was a weak game in my opinion
Morrowind: perfection, only marred by bugs, several questionable game design decisions and some graphical assets that were horrible even by those days standards (modding ftw)
Oblivion: horrible, only saved by active mod community
Skyrim: A LOT better than Oblivion, great world, but a tad too simplistic and shallow.
Skyrim is the pretty girl of the bunch that is fun to date but a nuisance to have around in a long run, because you don't have anything meaningful to talk about and every conversation with her is short and a bit boring

Morrowind is the gray mouse type, that maybe isn't such a looker, but when you get to know her better, you'll have time of your life.
So yeah... I still go with Morrowind on this one.
And believe me, I thought for long about it, its not just a "nostalgia thing".