Enamel contouring and bonding or 4 top veneers? (photo)

You have experienced bonding and have seen it last for 15 years.  Materials are better today and with a good experienced cosmetic dentist, you should be able to get an excellent result with bonding.  In my opinion, the biggest advantage of bonding is that you do not have to remove any healthy enamel.  It is a  less invasive procedure then porcelain veneers.   That being said, the drawbacks are that bonding is not as strong or stain resistant as porcelain veneers, and will not have as long a life expectancy.   Porcelain veneers are also much more expensive than bonding, but if you get a very experienced and competent cosmetic dentist, you should get a dazzling a result that will last a long time. 

I couldn't agree more! You have beautiful teeth. Have you considered orthodontics or clear aligners to reposition these teeth, followed by some reshaping of the enamel? You are smart to be concerned about the long term effects of veneers. They are a great solution for a number of situations and if done correctly they can involve minimal loss of tooth structure; however, there is nothing better than your own natural healthy tooth structure.
I understand your dislike of the dark space between the front teeth near the gums. You might consider having this area evaluated by a periodontist to see if there is a thicker amount of fibrous tissue here preventing the gum tissue from filling that space. Sometimes it can be thinned to allow it to adapt to that area better. 
Regardless of whether the space that you are wanting closed is done with bonding or veneers, there will still be a stair step effect that you will be able to feel when you floss that it will be necessary to keep exceptionally clean to prevent inflammation and/or decay. I think it is worth considering straightening your natural teeth and consulting with a periodontist about your options for relaxing that area of gum tissue.