There are advantages to both porcelain veneers and composite resin veneers. Your dentist will discuss which one may be best for you.
With porcelain veneers, thin shells of porcelain are shaped in a lab based on a mold of your teeth, then affixed to your teeth in a second appointment. Composite resin veneers are molded and shaped directly onto teeth that have been slightly etched, then hardened and polished, all in one visit.
Porcelain veneers require a second visit. On the first visit, a very thin layer of your teeth is removed, and a mold taken of your teeth, for custom veneers to be created at a lab. You will be given temporary veneers in the meantime. On your second visit, your porcelain veneers are cemented on. Porcelain veneers last longer when compared to composite veneers. They are highly stain-resistant, so you don't need teeth whitening afterwards. They are permanent and irreversible. Porcelain also has a beautiful translucent property that makes it look almost exactly like natural teeth.
Since composite veneers can be completed in one visit, they are faster. They require minimal preparation. The resin is matched closely to your natural tooth colour, or slightly lighter for a teeth whitening effect. Composite resin veneers may not last as long as porcelain, but they are much easier to repair. Composite resin veneers are also very natural looking.