not knowing where you are or the frequencies of the control channels you're trying to hear, it's hard to say. If it's in/around the 800mhz range, the RS 800 mhz rubberduck is an inexpensive and effective upgrade, though performance will degrade a bit on other frequencies. For close in towers, it won't be a problem.
More antenna choices are always better...many guys have far more antennas than scanners to optimize their rig to the need at the time.