Rfactor 2 is poor, really sloppy unfinished mess of a product. I think it's destined to fail in a big way now Assetto Corsa is on its way.
GSC2013 is good but pretty dated due to the old engine they use
Assetto corsa and Iracing are the way to go, both get updated regularly. I think Iracing is considerably better though, tracks are better for starters (ac tracks feel lifeless in comparison when it comes to ffb)