Bruce Wilderman, DDS

There isn't a lot of information in the photo, but it appears to be normal translucency of your teeth. Typically when someone has thinning incisal edges of the front teeth it is due to wear from grinding or excess acidity in their diet/reflux. In the limited amount I can see from the photo, that doesn't appear to be the case here. I would not be concerned about the teeth breaking. I think the likelihood is near zero. In almost 40 years of practice I can't recall someone breaking a tooth from a situation like this. Stop worrying about that. If you aren't happy with the appearance, that is another story. It can be restored to look differently.

I am not an expert in botox, but it looks to me like the muscles on the right side of your face are pulling harder than the other side causing the asymmetry. botox might help in the hands of an expert.

It's very hard to say from the photos why someone would suggest full crowns for your front teeth. I can see is that as a result of your ortho treatment your upper incisors are rotated and flared slightly. Because of this, the proportions of the central and lateral incisors look wrong, probably causing your dislike for them. There probably wasn't enough room to get those teeth in their proper alignment at the time of ortho treatment, so this was the compromise that was made. I would like to see you in person to better understand the situation. It could be that four bonded porcelain restorations of the upper incisors would be better able to adjust the proportions of them. Combine that with some whitening and you will have a great smile.

I think what you are really asking is which restoration will hold up better over time.  All three treatments (crowns, veneers and composite) require you to bond those restorations to the tooth using a composite resin.  It's always preferable to bond these restorations to enamel rather than dentin.  The bond strength to enamel is much higher.  

As far a longevity, Crowns and veneers will last much longer than composite resin.  In general crowns and veneers will last about 15 years, composite around 5 years.  That being said, it all depends on how you define "last". Composite will stain over time depending you your diet.  Sometimes composite can be polished and repaired to extend their life.   On the other hand porcelain restorations never stain.  When they fail, it's usually catastrophic (fracture).  You then have to replace them.  

Hope this answers your question.

I would agree with Dr.  Silberman's answer 100%.  Done properly the restoration should last a long time.  As he said the bite is the critical factor of whether or not the restoration will hold.