Why does this debate always come up, again and again
and again? Anyway, I think Morrowind's system is universally preferable over Oblivion's in implementation, although it itself could do with some revisions. First off, it'd be neat if we had FO1/2 style random encounters (ideally
within the game world and not instanced areas) in which your caravan/ship/Silt Strider could become intercepted by bandits, a pack of wild animals, et cetera. Your options are either to fight or high tail it to the nearest safe haven, leaving your colleagues to their doom.
Of course, I never saw Oblivion's fast travel system as some stupid "magic map that takes you wherever you want to go". It's really just a time lapse to simulate realtime travel on foot/horseback, with all the monotony cut out. I do agree however that being able to travel anywhere immediately was a bit much, and arriving without complications was also somewhat illogical. I wouldn't ask for a total return to Arena/Daggerfall's fast travel, simply because they were designed with larger worlds in mind and they'd be overdone in the more contained TES games we have now.
However, in the event that Bethesda does bring back this system of fast travel (hopefully with FO3's limitations, and side by side with Morrowind's service networks), I think it should be really dangerous. Your character could risk getting ambushed, ill, and the like, so it'd really only be for emergencies where getting to a town or travelling on foot is problematic. Again, I prefer to think of Oblivion's system as a fast-forward button on you travelling there yourself, and that in itself isn't too bad - but yes, it has to be made less forgiving.
Knowing Bethesda of course, it'll be one or the other - in which case I'd have to say Morrowind's system would be preferable.