Of all the classes, Arcanist is among the best for going the pure single class route. If you find specific skills aren't working with your class build or you want to try a different path down the skill trees, don't forget you can un-learn skills at a spirit guide (in Devil's Crossing, the spirit guide Sadhina is found in the top corner of the prison area).
We've listed out every possible Grim Dawn class combination in the chart below, followed by a closer look at some of the most powerful (or fun to play) mastery combinations available. While it's possible to run a pure single class (focusing on the mastery bar and fully upgrading specific skills), frankly it's more fun to try to find a dual class that works by meshing together opposing skill combos.
Besides the dark setting, what further sets Grim Dawn apart from the pack is in the dual class mastery system, which lets you tinker with dozens of possible class combinations.