I actually find Rogue not the best. My top four would be chanter, paladin and monk and wizard.
Why Paladin good sir?
Because of the high armor and very good heal options. Herald is one of the few classes, that can solo everything.
It's impossible for a herald to kill Dordu but it will tank him forever. Same goes for the slime, can tank it forever but not enough damage to go for the kill.
There's a video of a herald soloing both of those encounters, using the skeleton chant for Doru and splitting the slimes with the weapon summon.