Of the three detectors you mentioned, the X-Terra 50 is the ONLY one that offers manual Ground Balance in both discrimination Patterns and the all metal mode. Having the ability to adjust your ground balance can be a crucial factor in maximizing the performance of a detector. Especially in the wet / dry beach scenerio you mentioned. Add to that the ability to use either the medium frequency 7.5 kHz coils, or the higher frequency 18.75 kHz coils, and the choice becomes more clear. You can't beat the X-50 for your applications. Unless of course you were to include the X-70 into the mix. Tracking, Beach mode and Prospecting mode are three additional features offered by the X-70 that you might benefit from. JMHO HH Randy