Well 30" is the recommended length of an am/fm mast but I really don't think you can notice a difference on FM stations. AM is probally a little more sensitive to mast length changes. As long as you can listen to your favorite tunes leave it at the length you like best
Believe it or not, it depends on the frequency of your favorite radio station.
The optimum antenna length can be determined by using one of these formulas:
To figure a quarter-wavelength antenna in feet, divide 234 by the frequency in MHz.
To figure a half-wavelength antenna in feet, divide 468 frequency in MHz.
To figure a full-wavelength antenna in feet, divide 936 by the operating frequency in MHz.
Convert to inches using the usual formula.
A quarter-wavelength antenna is the minimum-size antenna. A half-wavelength (or greater) provides better reception. Five full wavelengths provide the optimum antenna length for any given frequency. If you have the room.
