Warriors are fine with a high CC group, such as 2x mage + warlock + Priest (2 poly, seduce + fear + banish, shackles), or Hunter, Mage, Warlock + Priest (Ice trap + Feign Death, poly, fear + seduce + banish, shackle).
In these cases, they can do their job as excellent 1 or 2 mob tanks. However, the muster of skill required to manage these setups is quite high.
Shaman have almost zero CC ability, and while they may be able to tank 1 elite while the warrior deals with whatever he's got agro on, this will fail horribly in Heroics.
I leveled a druid up with my shaman, and while the druid is VERY good tanking up to 3 mobs (better then an equally geared paladin imo, as Druids have higher damage mitigation), it becomes more and more difficult as you attempt instances with larger-then-3-pulls.
The only issue at that point, regarding Heroics, is gearing up your paladin for them. This requires doing the 70-instances on normal repeatedly until you have suitable gear for your paladin.
So, as from my experiences, Warriors are suitable for high CC groups, Druids are good to reach 70, with 4 shaman, as a tank, but are difficult in Heroics, Paladin are suitable for a 4x shaman group as tanks for all PvE occasions.
Also, there are many threads describing this. Please use the Search function next time.