Within the US, northern Mexico, and the major population centers of Canada, both signals can be received reliably, but local noise and interference conditions may affect your choice. WWVB is the better choice where the antenna placement does not allow a good view of at least half the sky, and in some communication sites where local transmitters interfere with GPS reception. Antenna cable length can be a significant factor in some locations. WWVB systems can use a one-kilometer cable or longer, but GPS is limited to about 100 meters due to the high frequency of the signal, unless extreme measures are taken. In a majority of systems, the antenna can be fairly close to the receiver, but a site survey should be made before making your choice.
Cost becomes the deciding factor when none of the above factors govern.
Q. GPS is a new, modern satellite system, and WWVB has been around for a long time. Hardly anyone doubts that GPS will be with us for many decades. Although the system is operated by the US military, and is subject to manipulation during severe national crises, its widespread use in many critical civilian systems make it politically very difficult to limit its use by the public. WWVB, although an older system, is receiving new levels of commitment from its operator, the US Commerce Department. Widespread commercial uses of the system has prompted new investment in system upgrades during 1997 and 1998.