iRacing if you seriously want to get on it Forza if you want to fool around and get bored after a few weeks
forza 7 is trash (btw I own the game). iRacing is just expensive but if I was offered both Iracing is the best option. I would even consider them competition as Forza is an Arcade/sim racer and Iracing is full sim
iRacing is a sim you get more for the matchmaking experience than anything else, and there’s a lot more cost involved with it.