[Iarhen]

Yeah, Vilya was the mightiest.

Nenya was the principal ring.

U should see Legola´s answer to the question... he makes a great comparison of this situation with a similar one between Melkor and Manwe. Even though Melkor was the migthiest, Manwe was the principal vala.

So, in the end whos the more important? Manwe

The same analogy applies to the differences between Vilya and Nenya

BTW
Another power for Nenya was the fact that it enhanced Galadriel´s magicks. For example, she was reknown for having the great ability to perceive the internal thoughts of people... Nenya boosted that ability, and she was able to read what Sauron thought about the elves. Thats something Elrond did not have, and something Vilya could not boost...

And again, in the U. Tales, its stated that the Witch King of the Nazgul did not dare to approach Lothlorien because of Galadriel´s fences (Ive always thought of this as a girlde, like Melian´s, but keeping all proportions). I bet those fences were upgraded by Nenya, since its power was to mantain Galadriel´s home beautiufl, one of the things it had to do was to keep all kinds of spoilings and destroyers outside her house... Including the Necromancer, the forces of Dol Guldur, the Nazgul and all the things inside Moria (orcs, balrog, trolls, etc).