My favourite is GT3, for sentlemental reasons.
I am playing through GT3 with an emulator, running 4K resolution and my T300 wheel ... for me it's the probably the way to enjoy GT3 at the highest level that I never thought possible 20+ years ago.
I love the bright & bold graphics, it's detailed enough to project some illusion of speed and excitement on a race track, but not too much detail, i.e it is romanticised and leaves more to the imagination rather than a explicit/clinical showcase. The same reason why I prefer Sega Rally 1 & Daytona USA 1 vs their sequels.
The simple to use "arcade" style UI as it gets you right into the action. GT4 is technically superior, however has that menu UI bloat and softening/haze effect on the visuals that puts me off it most times.
GT7 is a sham.