Yea, Hunter would have to be one of the fastest aside from Death Knights starting at 55.
Ranged naturally helps prevent a lot of issues in the combat routine.
Stucks being a big issue given that some mobs may be standing up on ledges or rubble in which the bot can't navigate whereas being a Hunter you can just ranged them down.
Some areas where these stucks happen, I've had the bot stall for up to hours when left unmonitored and as melee this could happen a lot more frequently.
Hunters also die a lot less than other classes given their PvE hybridization (pet tank, spirit bond heal, and efficient DPS).
With this they can also multi-pull at a lot more mobs at an optimal rate which in turn helps with 'experience-per-hour.'
The only potential issue(s) I've ran across is that Singular will use Disengage in bad situations which causes the character to fly off mountains or into larger packs of mobs.
So you may want to turn that off in questing areas where it may be a problem.
Also, Singular likes to use Deterrence a lot more than it should - disregarding player health. You may also want to turn that off.
On the flipside, Shadow Priests would have to be the slowest given that after any fight the bot will want to Drink for mana instead of attempting mana restoration spells and that Shadow Priests are absolute mana sponges.