What is the best hospital in usspecialized in vascular surgery?

Several. There are several in the us. Also depending on the vascular condition there are some that can be better than other. Need more information and specific condition. Also location in us that you live.
Depends. It is more often surgeon rather than the institution that determines how good the vascular surgery is. Surgeons who personally follow there patients, pay attention to details, and communicate with there patients tend to have better results. Talk to patients who have been operated on by the surgeon you are looking at to see what their experience was.