My personal opinion is that an 05 V6 Mustang
is a great first car. It handles well, (and can be made to handle even better). It will save you a couple of bucks in insurance over the GT. Parts are plentiful. All around, not a bad deal. No you won't win any races (stock) against your GT neighbors, but then again you don't need the tickets either.
I currently drive an 05 V6 convertible as my daily driver and love it. But this is far from my first Mustang. My first was 1968 GT Coupe, 390, auto trans. (Wish I still had that one). But I love my 05 vert.
Enjoy the ride!