I loved Gran Turismo 1 (i still have my copy & the disc still smells of the rubber smell they put on the disc) GT2 & GT3 were also good, i didn't like GT4 & i hated GT5 (like a fool with more money than sense i got the Signature Edition (my most regretted game purchase ever).
On my Xbox i got Forza as i really like racing games & it was great, & so was F2, F3 & F4 i got my X1 late so was behind on F5 & it isn't as good as the previous incarnations, but it's still good.
I have had a few racing games on my PC & i had Pcars on PS4 but i traded it in yesterday (for funds for Forza 6) now Pcars is a very good game, but like the GT games (other than GT1) i just didn't enjoy it as much as i do the Forza games.
I will never forget playing Gran Turismo 1 one night, i was doing the last race on the Special Stage 11 i was in my yellow Mitsubishi GTO LM Edition on soft tires & they gave me the edge to pull out enough of a lead so i could pit & come out in-front of the Toyota GT Ones that were on the hard tires so could do twice as many laps as me on the soft's, the adrenalin was pumping as the laps rolled down & i knew i was going to win & when i crossed the line in first place i just sat back in my chair & relaxed after the race of my life, i have never been in a real car race, but what i felt that night is what i imagine it would feel like for real (more more intense in real life though) i felt like Jezza here (at the end of the race)
top gear enters britcar 24 hour endurance race i just wish there was a racing game now that could give that same feeling as that final race, i never played Gran Turismo 1 after that as i had completed it & i just needed to win that final race.
I have the most fun playing the Forza games, i know they are not as sim like as Pcars or Real Racing 3 & Gran Turismo has more sim like options, but they just don't have that same feeling for me like Forza does, the original GRID Motorsport as did RAGE Racer also had a similar feeling, it just made you (me) want to play more.
Arguing over which racing game is best is pointless as people like racing games for different reasons, some people like tweaking & setting up cars & there are people like me that will just drive hard & fast & go beyond the limits, sideways round the corners, & crossing the finish line in first place with a smashed up car with my hair on fire (Top Gear style).
Off topic but this is the best car in any racing game ever.