Oblivion is enough of a disaster implementation-wise that technically having greater mechanical complexity doesn't concern me in the slightest. And Oblivion's writing is, to me, a low point in both the series and Bethesda's body of work as a whole. Skyrim's writing isn't amazing, but the moment-to-moment gameplay being less frustrating gives it the win for me, between the two.

Morrowind is great, though. Probably the best world building I've seen in a game.