If I could have only one pan in the kitchen, it would be a cast-iron skillet. There’s almost nothing you can’t cook in these things, on the stovetop or in the oven. It’s the perfect pan to roast a chicken in, or make a sauce, or sauté a steak, or stir-fry vegetables.
It’s helpful to have large and small saucepans and sauté pans. And nonstick pans are wonderful for cooking eggs and crêpes and other delicate things that can stick, but they shouldn’t be your default pan. Invest in one good nonstick pan and keep it clean and protected. I either hang mine or put a kitchen towel in it in the cupboard to prevent other pots and pans from scratching it.