This website has my favorite builds for each class. Each build shows two possible weapon combos, with the top combo being my preferred combo that I actually use in game. The screenshot of the reject on the right is a screenshot of my cosmetics for the class. Everyone knows that each loadout should look different from all the others. I also use different weapons on each loadout that don't duplicate with any other builds so I have the most variety possible.
They loadouts are listed in alphabetical order, rather than based on how effective/fun they are.
If you use any build other than these you are wrong and should feel bad.
There is an excellent guide from Reddit user /u/CommissarTyr that goes over every damage type each enemy has. Many enemies in this game have multiple damage types, depending on where you hit them. There are also different damage multipliers, depending on where you hit each enemy. Visit it HERE.
Another obvious resource is the Meat Grinder inside the game. It really lets you test your weapon breakpoints to test what type of modifiers you should bring on them.