Steel bearings are the everyday standard for skateboarding because they are practical, widely available and easy to replace. Ceramic bearings use ceramic balls, usually with metal races.
Steel
Steel offers dependable performance at an accessible price. Keep it dry, clean away grit and use a small amount of skate-safe lubricant.
Ceramic
Ceramic components can resist some forms of corrosion and may feel smooth, but they still need care and correct installation. They are not maintenance-free or automatically faster.
Pick the material that suits your budget, riding conditions and willingness to maintain the setup.