For riding on mixed surfaces I'd suggest something like 70 front, 75 rear as a starting point then try a few rides and adjust it for personal preference (within the limits stated of course).
Good recommendation there from Phil to have a few more psi in the rear, where most of the weight is.
Don't get too hung up on one or two psi here or there, but you will probably be able to tell the difference if you go up or down in increments of 5 or 10psi.
A change of 10psi can make quite a difference to the harshness/softness of the ride.
The higher the pressure, the less likely the tyre is to puncture.
That's a factor - but only a factor - to take into account when deciding what pressures you like best.