I bought this game a couple weeks ago on the Deals with Gold sale. What is the best class to start with? I have no history with the series.
There really is no "best" class. Pick one that speaks to you and go from there. They all handle differently and are fun in their own right. If you don't like the class you started with after ~20 levels, then start a new one. Classes I didn't think would be fun when I first started playing many moons ago I would come back to later and have a blast with.
If I had to quickly sum up the general idea of each class, to help, I'd do so as follows. Though each class is very versatile, in spite of my generalization.
Barbarian: "Tank" class, up-close and personal approach.
Wizard: Glass cannon. Puts out major DPS, but is squishy.
Monk: Melee with style.
Demon Hunter: Ranged, with fun pets. Has dual-resource management, the only class to do so.
Witch Doctor: Pet summoner. Uses earthly supernatural abilities.
Crusader: Can be up-close or ranged.
Necromancer: Pet summoner. Uses the dark arts for their spells.