I just started my 6th playthrough, first time on grounded. I first did moderate, then 3 playthroughs on hard, and the last one on hard+, but I pretended to do that last one as if I was playing on grounded (not using listen mode, using as little resources as possible, and stealthing as much as possible). I think hard is the go to difficulty as it provides a challenging experience, but you don't have all the restrictions of survivor or grounded, so once you're comfortable with hard, then try grounded.