I'll give you some of my thoughts on the subject :
First of all you have to meet a good player in all those classes -feral druid,enhancement shamy,warrior,rogue,retri pala
Because you're objectivity turns subjective if you don't- an example you can have a good shamy or retri owning all others and thinking- G that class is the best.
Through my experience (which is vast in this bracket) :
1.The strongest melee class is a retri pala cause he hits like a warrior and has stun & lay on Hands & the ability to self heal -and not to mention much armor to stay alive.Also retri palas with all there CD's are the most dangerous but they have to watch our for there small mana pool,else it's all over for them.
2.Ferals like rogues have a lot of mobility and there first attack hits like a mofo but are squishy so they can't stay alive for long.
3.Enhancement shamans are the most interesting class cause of there diversity but are mana dependent and can only move across a small area in a fight (due to there totems) and they have a nice DPS burst.Also they can either do DPS or self heal while being hit by some other heavy DPS melee class,so when there mana runs out it's pretty much over.
4.Rogues can only be efficient from stealth and after that it's the ''run for your life story'' if there ''Evasion'' is on CD.
5.Warriors have the greatest dmg and most armor,can stance dance if needed and even kite some melees with piercing howl ,and with a good healer on there back can become an unstopable force with the most mobility (even more then hunters on an ocation)
Concirning duels warriors are the strongest (beats shamys,rogues,ferals) only if they can suprise a retri pala in not outhealing himself in first 6-8 seconds of the fight then it's a gg-else retris wins the bracket as the strongest melee DPS class.
Hugs, kisses, and broken fingers,
Alphasky