My two front teeth are bigger than the other ones. Veneers or Invisalign - Braces? (photos)

If your main concern is the size of your teeth, then porcelain veneers would be the best way to change that. Orthodontic treatment will move the positioning of your teeth, but won't change the size.  Porcelain veneers can make your teeth look smaller.  I'd recommend possibly doing 4 so that they look more proportional.  The lateral incisors (next to the 2 front teeth) will be made to be slightly larger, allowing for the front two (central incisors) to be made slightly smaller. Overall, it would look more proportional. Hope this helps.

If your main concern is a tooth-size discrepancy, I would recommend starting with advanced composite bonding. This can even be done as a non-bonded practice or "mock-up" with most experienced cosmetic dentists. Your concerns may be as simple as altering the shape of a central tooth slightly, or adding dimension to your lateral teeth to make the central teeth look less prominent. In most bites, your lower teeth tell your upper teeth where they should be, so sometimes treating this orthodontically can be challenging. It may be smart to seek out a cosmetic dentist that also understands and performs orthodontic procedures. Veneers can be beautiful, but can be especially damaging to your natural teeth  when you're trying to make something look smaller.

Orthodontics in any form (brackets or Invisalign) change the position of the teeth, but do not change the SIZE.  Plus, it takes time.Porcelain veneers can improve the size, color, and shape of your teeth in just 2 visits.