In the end I spent most of the time between The Shattering and Cataclysm playing two characters: A troll warrior and a tauren paladin. They were using similar degrees of twink gear, both went for their respective tanking talent spec, and after 15 levels of soloing concentrated on tanking with random pickup groups. Assuming that my tanking skills don't magically change when I switch from one character to another, and seeing how their gear was similar, the difference between these two characters is astounding. The warrior barely manages to keep aggro in multi-mob situations, and always comes in 4th place on the damage meter, just above the healer. The paladin plays like ultra-easy mode, tanks any size of mob group without ever losing aggro, and more often than not comes out on top of the damage meter at the same time. It is really ridiculous! And depressing for my warriors, not just the low level one, but also my level 80 by extension.
The differences between paladins and warriors are already quite visible when they choose their tanking spec at level 10. Warriors get Shield Slam, which is a melee range attack, hits only 1 mob, and often can't be used early in combat because the rage is lacking. Paladins at that same point get Avenger's Shield, which deals twice as much damage, then hits up to two more mobs, has a 30 yard range, and is perfect for pulling even casters, as it silences them. When soloing I one-shotted quest mobs with Avenger's Shield crits. Having that much better pull spell enables the paladin to grab a lot of aggro quickly, and keep it. The warrior needs a more complicated and less effective Rend + Thunder Clap for AoE aggro, with a much shorter range.
Besides getting aggro, the paladin also has the much better survivability, having two instant self-heals, versus none for the warrior. Between Word of Glory, which can be used several times in a combat, and Lay on Hands, which heals the paladin to full, I even survived big combats where the healer had lost connection. The only consolation for the warrior was that at least Blizzard nerfed the paladin's taunt to be identical in function with the warrior taunt. Previously the paladin version dealt damage, and the warrior version didn't, now both don't.
Now you could say that the lack of balance between low-level warriors and paladins doesn't matter. Both characters are strong enough to solo quests, and given the tank shortage it is unlikely that a group will votekick a warrior in the hope of getting a paladin the next time. But as far as I can tell, paladins are still far superior tanks to warriors in 5-man groups at level 80, and I'm not sure about which of them would be preferable in a raid now. Right now I'm hard pressed to find *any* role or environment in which I would rather have a warrior than a paladin. It really feels as if Blizzard hates the warrior class, and I can't understand why they would so obviously disadvantage them.