One of my friends has an Aston, and I was sort of shocked by how bad it is. Watching Top Gear you would think they are marvelous sports cars, but in real life it's a huge let down. It's big, heavy, soft, it feels sluggish. The dash just goes for miles. I sort of felt like I was in a Crown Victoria or some big old American boat.

 

Not sure if you are joking or not, but I consider the vantage to be more of a sports car then a GT. I consider the 650, bently GT, cl550, and other heavy/comfortable 2 door 4 seaters as GT's.
But the world calls 911's sports cars and people on this forum call the 911TT a GT car instead of a sports car b/c its on the heavier side then the rest of the 911s. So it seems there is some gray area not all black and white.

 

Technically, both Vantage and C2S are Grand Tourers. A sports car (by classic definition) is a two seater with a convertible top. A Boxster is a sports car, so is Mazda Miata or Lotus Elise. C2S or C4S are not. 997TT base on the high performance can be classified as a Supercar (along with 458 Italia, various Lambos, etc). Also, Carrera GT and 911GT2 fit in the Supercar category. Based on all this, comparing C2S with Vantage or DBS/9 is fair.