Hands down, Forza Motorsport is the best game. I don't get the shade.
I have been playing this since last year and damn I live it
I have Assetto Corsa, but it just doesn't feel as fun. I'm not sure if it's due to my G920, but I feel the car much better in Forza Motorsport, whereas Assetto Corsa seems too light. Plus, the servers I enter in Assetto Corsa are often empty (and I do have cross-platform turned on).
I have seen a lot of shade thrown at Forza Motorsport, but I just can't get why. Yeah, sure, you can't adjust a few things on the fly, but you have more than enough to have fun. The track cycles are really nice, and the servers I get into are full most of the time-especially in the GT3 and GT2 series.
When it's Nürburgring, it's guaranteed fun. Sure, you get hit in the back and dropped to last position, which sucks, but grinding from 19th to 8th over 3 races is mad fun.