Radiology is less competative than Ortho, but more competative than Gen Surg.
So, if you want to try the Vasc Surgery route, you would need to get a Gen Surg residency and apply for a Vascular fellowship. I don't know how competative those fellowships are, but my guess is that it's not too bad.
If you want to do IR, you need to match into Radiology, and get an Interventional fellowship, those are easy to get (like most rads fellowships).
The competitiveness is about the same, people don't want VS as much b/c the lifestyle is rough. People like rads but worry about turf issues and lack of direct patient contact, plus there are a ton of spots in the match so it's not as tough to match as some think.
The real issue is do you want to be a surgeon. Do you like being in the OR, sewing the tiny vascular anastomoses? Both IR and VS do cath lab work, so that is a wash. Would you rather be reading images with the rest of your time or doing surgery, rounds and clinic. Both are well compensated. Do a VS elective if you are unsure.
One other thing about VS is that they have damn sick patients, all with terrible vascular disease making them highly unstable. Repeat surgeries are the rule here. Complications very common, do you like amputations? I've yet to meet a VS patient who does smoke or didn't just quit (supposedly).