I have some pretty in-depth ideas on the subjects of enemy/loot scaling and leveling, but it would take a lot of time to really lay them all out so I'll try to keep it brief.
If I had to choose between a game with no scaling/leveling, and one with scaling/leveling similar to Oblivion's, I'd definitely choose the former. However, I think that as a few others have said, the ideal is some minimal scaling and leveling in certain circumstances, along with established areas of relative safety to contrast with more dangerous areas.
I think that the main quest line should have some scaling/leveling for the simple fact that the player shouldn't be forced to grind or develop outside of the questline to be able to finish it. It should be possible to attempt the main quest at low levels, though there should be parts that are very difficult. And if the player waits until a higher level to work on the MQ, it should be somewhat easier but not so much so that it becomes boring or pointless.
Outside of the MQ, leveling and scaling should be very minimal. A level 1 char should be able to encounter any type of foe in general, as should a level 40 char. A level 1 char should be a bit less likely to come across super strong foes in areas of average danger, just to make it possible for low level characters to explore at least some of the game world in relative security. Also this gives higher leveled players a bit more incentive to explore these areas, as they'll get better loot/drops from the enemies they encounter. I don't think that there should be a drastic difference between the average strength of foe encountered by a level 1 char and the avg strength encountered by a level 40 char in these zonez of moderate danger, just enough to find some balance. In very dangerous areas, strong foes should be extremely prevalent regardless of character level, so only a high-level character could survive for long. In general cities, main roads, and communities should be relatively safe, meaning you encounter fewer monsters in these areas (or none at all) and any that you do see will almost surely be pretty weak.
Regarding treasure/loot, there should be more handplaced loot in chests and at the end of caves and ruins. There should still be some randomly generated loot sources, but the leveling/scaling should be drastically toned down. It shouldn't be possible to find Daedric Armor in random loot. The amount of money a level 1 char is likely to get from random loot should not be supremely less than the average amount of money a level 40 char is likely to get, but there should be a small difference... Like 10 coins or so; hardly noticeable, but just enough to slightly favor those who take the time to build up their characters.
In short, I think that parts of the world should be essentially impossible for all but the strongest players to access. I think that there should be rewards for taking the time to build a strong character, but that they should come from handplaced loot in dangerous regions rather than a better chance at valuable randomly generated loot. And I think that in general, a high-level character should have less trouble playing through the game, but that it should never become a cakewalk, which means that there probably needs to be scaling to a certain extent, but that it should be as minimal as possible.