Vintage or used is always a better deal. New bicycles, like new cars, lose a significant amount of their value the moment you take them home, and depreciate steadily for some time. In the case of the more trendy and more perishable nature of new bikes, depreciation is an even worse problem. My old Colnago C40 has lost more than half its value, and I don't expect it ever to increase. The carbon fiber frame is bonded with plastics which degrade over time, the gel coat has already yellowed over time, and the joints where the aluminum dropouts meet the carbon fiber are prone to corrosion.
On the other hand, I have a 1980 Masi Gran Criterium, which cost $1800 brand new. I could sell it today for $1800, though $1800 in today's money is not worth what it was in 1980.
If I were to buy a new bike, I would look for circa 2000 Schwinn Peloton or Lemond 853 steel frame. These are phenomenally well made, are great riders, and are priced today below what they are worth. You get sharp handling, and a supple ride. They aren't as sexy as the current curvy and swoopy carbon fiber frames, but what is hot today is not tomorrow. When I was a kid, people had so much hair they made Chewbacca look like Curly from the Three Stooges, shirt collars which were long enough to tie over the tops of their heads, and bell bottoms which flapped in the wind as they walked. An old steel frame is like Levis 501 jeans, or Ray Ban sunglasses, not trendy, but never uncool.