If the Match numbers from 2006 are any indication, vascular is more popular. There were 23 or 25 (I can't remember the exact number) more applicants than spots. In 2005, the applicant number almost equalled spot numbers, and I did not see that the number of spots decreased (thus falsely increasing the number of unmatched). 2005 had 25-30% progams unfilled, and 2006 had 5 or 6 spots after the Match.
In any case, I am starting a vascular fellowship in July, and I think it is great. I can't predict easily what my schedule will be, but with endovascular (and therefore shorter hospital stays), I anticipate more time operating/doing procedures and less time rounding on a floor full of inpatients. One of our attendings works alone at his hospital, and while he is busy, he says that the hours were much worse in fellowship (yeah for me since I am going to his alma mater😱 ).