PS 4 you can go for Gran Turismo 6 play the license challenge
xbox one - go for Forza Motorsport not into details whats the next forza will look like if they will stick with the GT thing where there are tons of cars but since its xbox version of GT maybe they will so not highly suggesting you to get this one
games you can play on both console
NFS: Shift 1 and 2
Grid 1 and 2
Test Drive unlimited 1 and 2 - more on exotic cars no tuners
Dirt - if you like rally cars and going sideways
F1 racing - more on F1 fanatics