If I had to peg a single number, I would say 750. You want your scores to be high but not too high and you never want to end up in the red where they are bad. You will struggle to get loans and financial help everywhere you go with bad scores.
The higher the better, obviously. I think having 800+ is ideal and a goal we should all strive to get to. Far too many people have bad credit these days and it really impacts what you can and can't do in terms of buying properties, renting, or purchasing a vehicle.