Hello, and thanks for the in depth inquiry. Of the three models you mention, I believe the best all around machine for your wife would be the Vaquero. The Tejon, Vaquero, and Cibola all feature the HOT "High Output Technology" circuitry. HOT simply punches a stronger signal into the ground and amplifies the returning signal to a higher level, compensating for signal that is lost in the ground between transmit and receive. The Tejon's amplification is slightlky greater than the Vaquero and Cibola, thus, in highly mineralized ground it tends to run some what more on the "ragged edge", and can cause some erratic sounds. Those who just want the greatest depth possible realize that when pumping that high of an amplified signal, some noise will be present as well, and are "all right with that idea".
Other's want as much penetration as possible, but prefer a smoother, more stable sounding signal. The Vaquero and the Cibola fall into the latter category. While punching a stronger signal into the ground, the amplification on the return signal is slightly less, and runs smoother as a result. The Vaquero's advantage over the Cibola, while running on the same circuit board, is that it offers a 3 3/4 turn manual ground balance control as opposed to the automatic ground control on the Cibola. Die hard relic and serious hunters love the ability to manually set the ground control for specific sites and soil conditions.
While the Vaquero is also a turn on and go detector, as is the Cibola, it affords a little finer control of mineralization rejection.
I have used the original Tesoro ElDorado for years with great success. The Vaquero is everything the ElDorado was, but in a much lighter package, with much higher tech electronics to process the signals. These machines are the fastest responding (null to positive, bad target to good target) on the market. The result? You can sweep slightly faster, yet still pick up a coin, ring, or military relic lying within a half inch of a piece of iron, nail, or pull tab. Without the fast response, many are missed.
Sorry to go into such detail in this response, but I believe deeply in the Tesoro line, and the Vaquero is about as good as it gets. You can see some of the results from hunting with the ElDorado and the Vaquero at my website, www.treasurehut.org and clicking on the finds page.