There is not really a best source of protein. The first thing that will guide your choices is your own preferences and that includes ethics and morals. Then you look at what is available and what’s your goal. Such as if you’re wanting to increase your healthy fat consumption you’ll want nuts in your diet at a higher concentration than someone trying to reduce the amount of fat they are consuming.
As already mentioned if you eat a wide variety of fruits, vegetables, grains, nuts and beans and toss in some fortified foods you’ll be ok. Try to eat some raw stuff such as apples or bananas and not just cooked food. Try to eat more foods in their whole form versus box store processed foods. It’s ok to add in veggie burgers and so on. But don’t make junk food your staple.
with that said often the best source of protein is protein powder.