Arena is terrible
Daggerfall has the biggest map in any video game, ever.
Morrowind is everybody's "Nostalgic" favorite and because of this they all think it's the best
Oblivion is the "red headed step child" to most because they "made it too easy"
Skyrim got rid of the custom spells and further got rid of the creative elements of the series and made you more cookie cutter.
Morrowind is the best. The amount if stuff you can do in it is just crazy. I got tired if walking every where so I enchanted some boots that let me jump around like the Hulk.