[Edi]

It's highly dependent on the particulars of a situation. I tend to use the searching spells a lot and usually always research thaumaturgy 2 and evocation 2 quickly. You should use mages to search for sites early on. Later you can use the searching spells, especially if you have low gem income for those types.

If you're playing with a low site frequency, the spells are less useful because it takes longer to get back the gems you burned searching. If you have mages who have several paths. those are always good to use, because they search many paths at the same time.