Hard to Fathom..

[Gorthol]

Sauron gave the Nine to Mortal Men who proved easiest to ensnare.

I guess the Nine were less powerful than the Seven, since Sauron probably knew that Men would be easier to ensnare and corrupt (as it says).

The fact that Sauron could find the Nine but not the Seven, was only a coincidence or was due to the fact that the Elves of Eregion took greater care of them? What do you think?

It seems by the writings as if the elves considered the Seven more valuable. "There Sauron took the Nine Rings and other lesser works of the Mírdain;"