The Fisher "x" series were known for NOT losing depth when increasing the discrimination.
They also had very low frequencies : 1212x 4.2 Khz, 1225x 5.5 Khz, etc, which made them extremely good coin and relics hunting machines.
Modern Tesoros do have higher frequencies, and will be better on tiny jewelry, but still find the coins and relics.
Knowing that, well the choice is yours. If you want to hunt for clad, both will do. Deep silver and relics ? a"x" fisher, and if you want to hunt for small gold jewelry, the Vaq woud be a good choice
Amongst my fellow hunters here in Europe, many - including this Olewriter here- still use older "x" fishers with great success.
That being said, I am about to buy a Tesoro, but none of the "HOT" ones. Probably a Silver or an UK Rapier.
Let your choice be wise !
Grumpy