Which is bettter, bonding or Porcelain Veneers?

They are both good, but each has it's advantages and disadvantages. Bonding can enhance the appearance of teeth , requires no particular preparation. It can be used to restore cavities, and add to the contours of teeth. It is can be very natural in appearance and blends quite well with natural teeth colors due to its optical properties.
Bonding does have a problem that it doesn't hold surface detail as well as porcelain and can pick up stain especially when a patient doesn't have ideal dental hygiene. Plaque left on bonded surfaces can create porosity that can allow stain to attach to the composite material and also porosity can make the bonding appear 'water logged'. 'Water logged bonding appears to expand and stand slightly away from the tooth surfaces.

Porcelain Veneers are less able to blend in with natural teeth but still can create an extremely pleasing appearance. They are especially good for lightening and lengthening teeth. If made properly they can mask minor discolorations in the underlying tooth structure because a skilled technician can opaque the porcelain. They hold their surface glaze better than composite and are stain resistant. They do not require the dentist to be the"artist". Instead a dentist can specify an extremely talented ceramicist to create a new look for their patient. Free hand bonding requires the dentist to be the artist and although many dentists are extremely skillful, not all are capable of carving creating extremely natural bonded restorations. For them Porcelain Veneers can provide a more predictable esthetic result.

Porcelain veneers do often require more tooth reduction in order to not look bulky and are more expensive than bonding. Porcelain veneers usually take two or more visits, while a bonded composite restoration can be done in a single sitting.

In terms of cost, in my practice a free hand bonded restoration is about a third of the cost of a porcelain veneer. This is the biggest drawback of porcelain veneers. Many patients who might benefit from porcelain veneers opt for bonding for primarily financial reasons since 10 porcelain veneers can require a patient to spend in excess of $10,000. For many patients ,simple bonded enhancements can improve a smile while not 'breaking the bank'.