Sauron with the One Ring (Which made him even more powerful) was knocked down by his son Gil-Galad. Fingolfin crippled Morgoth while he was still stronger then Sauron, and was stated to be the strongest of the elves.
Anyway there is a quote calling Feanor the strongest and basically best elf in everything.
"For FŽanor was made the mightiest in all parts of body and mind, in valour, in endurance, in beauty, in understanding, in skill, in strengh and in subtlety alike, of all the Children of Iluvatar, and a bright flame was in him."
I look at Morgoth and Sauron similar to the Emperor and Vader. I think in time, Sauron would have eventually and cunningly plotted to betray his master and succeed to take the dark lord throne himself. Had Morgoth not had been banished to the void I mean.
I think if Sauron were truly powerful enough to be Morgoth's equal, or more, he wouldn't have served him. Despite all of his cunning, Sauron is a Maia and Morgoth an Ainu, so his service to the original Dark Lord was only proper. Also, Sauron was not the only number 2 guy that served Morgoth, either. It's thought that Gothmog was Sauron's equal, if not a close equal. The Lord of the Balrogs may have lacked the magic that Sauron had, but made up for it with his size, strength, and strategic military capabilities. Gothmog is certainly not a villain that should be overlooked.