Damage is far less important than strategy, and the best strategy is surprise, or range.
Summary:
bows > your ability to survive
You need to take into account some of the passive mcmmo abilities as well, and average their damage over the chance to be inflicted to gain a more accurate picture. Bows have a chance to ignite, swords to cause bleed etc
http://mcmmo.wikia.com/wiki/McMMO_Wiki
There are also armor set bonuses (not sure they are working ^.^) :
Unclothed gives a bonus to unarmed
A set of leather armor (ranger set) increases damage from the bow
Crouching/ sneaking - increases damage
With these taken into consideration, I would say the elves and their bows have the greatest potential to inflict damage, though their style requires greater skill and by far the most difficult training (aiming, especially with any lag is terribly difficult)
Perhaps you think, I am exaggerating. To illustrate;
At archery 1000, a sneaking ranger, well equipped would have:
* An effective range of 50 blocks
* 2 base damage
* +1 bonus damage
* +5 damage ignite chance (1.25 average)
So that's 8 damage or an average of 4.25 damage for each hit, and without a delay between firing, the ability to hit a large amount of people rapidly. In choosing the right vantage point, they can also be invisible.
Did I also mention all elves get yet another defense/attack bonus amongst trees?