If you're like me, you want to use NPC's with class levels in your campaign. But 5e balances PC's and Monsters differently to allow the player to feel awesome (monsters have a bunch of health, but lower damage, to allow players to get to use their special skills). If you just make a character sheet for, say, a wizard and put them into a battle with the players the results are more of a coin-flip.
For this reason I recommend the
NPC Statblock Compendium(recently updated). This guide lists all the NPC statblocks from the Monster Manual, Sword Coast Adventurer's Guide, Mordenkainen's Tome of Foes, and more, as well ass making at least one NPC statblock for the remaining PC sublcasses which are not covered by official releases. These NPC's are balanced more in line with the 5e designer's intent to allow players a fight that should last a few rounds, and not devolve into a save-or die battle, while slimming down the number of class features for a more manageable battle for the DM.
