If you hated GT5 then go with GTA5. GT6 has improved physics and a bigger car/track list but suffers from having gone backwards in some areas from GT5, and the basic game is unchanged so if you didn't like GT5 there is no reason you would like GT6.
I like GT6 but it definitely feels like PD need to stop spouting hot air about all the "features" and "innovation" and actually make it a reality. I feel like they spend so much time patting themselves on the back that they miss everything else going on around them.
Anyway yeah, probably GTA 5.