The easiest, yummiest, most convenient and cheapest? Yes, I'm asking a lot. I want to feed and eat plenty of food and fish, which would prevent me from eating if I wanted to.
Where are you from? What kind of fish do you have available? Are you catching or purchasing these fish? Do you cook or are you an amateur? I know I am asking alot but it takes more information to give you a good answer.
Cheapest. Most likely Tilapia. I think most people bread it and fry it. I like whatever fresh fish I can catch. Store bought we tend to get Salmon or catfish mostly. Catfish is fried, salmon gets put on the grill. Spices for salmon tend to depend on the mood. Sometimes something as simple as some citrus slices on top, to more complex with spice rubs.