For me, on PS4, Gran Turismo is on top.
I also (tried to) play Project Cars 2 but it’s just too much trouble to get going in it. You need to (re)boot the PS4 in a specific way or else the wheel doesn’t get recognized in game, the whole user interface is messy and sometimes doesn’t make sense, sometimes refuses to do things because you didn’t do something right or in the right order. When I somehow finally made it far enough to actually drive a car, it’s pretty much impossible to keep a car on track for more than 1 corner (all with basic default settings). PC2 just needs soooo much effort put in to it from the start to setup the game, your wheel and the cars it’s just not worth it if you just want to drive/race. Sure the game looks pretty good, the car selection it great and there are tracks in it I absolutely LOVE (classic Spa, Hockenheim, Rouen, Nordschleife). But it’s just too much trouble to get going so I don’t even bother anymore.
With GTsport you can very easily just get in and drive a car in minutes. Most cars might not be at its best with default setup but at least it’s a good point to start from. There are a few cars that are pretty bad to drive in default form, but the majority are pretty good. The menu change from GT6 was a big one but I got used to it quickly.
I also bought F1 2017 recently and to be honest, I only played it 2 or 3 times since. It’s very different from both GTsport and PC2, you can get in to it pretty quickly and once you get used to the physics it’s decent. But I think i’m just too used to GTsport, anything else feels weird. I wanted to love F1 2017 sooo much because i’ve been a F1 fan for over 20 years now and probably only missed watching races 2 or 3 times in those 20 years, and played many F1 games in that time, so I wanted to love F1 2017 so much I had extremely high expectations and it just didn’t meet them. As it’s a F1 specific game you can obviously only drive F1 cars and I’m just too used to being able to choose between various types of cars, it’s weird being ‘locked down’ to just 1 type.
Although difficulty and realism aren’t the same, they do tend to go hand in hand. As more realistic games tend to be more difficult but a difficult game might be just that because a lack of realism.
Nothing beats LFS though.