Personally, I feel DEF are very similar. No point paying for a D if a F is available. But once you go down to G, you can see a slight yellow tint, which is not obvious when viewed from the top, but becomes obvious when you look from the bottom of the diamond. However, once you set a G diamond, most people will only look at the diamond from the top.
At the end of the day, it depends on your comfort level and budget... Some people need their diamond to be a clean crisp white (DEF), and some are okay with a slight tint that's not obvious when viewed from the top (G).
The way angle you see and under what kind of lighting it affect your color perception too.
