Lots of variables to consider: riding style, rider weight, road quality, rim width, tubeless vs clincher,bike type etc. These days for the solo recreational riding I do, I use the widest tires I can comfortably fit on my 2 bikes, so 25c on one and 30c or 28c on the other. In general wider tires can run lower pressures so they give a plusher ride and are better suited for poor roads and even light dirt.