For a single like the PA28, a good rule of thumb for takeoff is to keep the nose very light during the whole takeoff roll, let the plane lift off when it's ready, hold the top of the cowling just above the horizon (assuming you are neither a dwarf nor a giant) and let the plane do the rest. You'll find that gets you pretty close to the best rate of climb speed - perhaps with a bit of tweaking with the trim.
You'll need to pitch for the specific speeds a bit more in twins and, depending on weight, might find wider variances in pitch angles post rotation.