The greatest Craftsman/Smith of Arda

[Belegorn]

Feanor forged the Silmarills and the 7 Seeing Stones among others.

"He became of all the Noldor, THEN or AFTER, the most subtle in mind and the most skilled in hand. In his youth, BETTERING the works of Rumil, he devised those LETTERS which bear his name, and which the ELDAR USED EVER AFTER; and it was he who, FIRST of the Noldor, discovered how gems greater and brighter than those of the earth might be made with skill" [68-69]

Feanor had all inhabitants of Aman in awe. That says something to me.

The Noldor were said to be, "the most skilled of the Elves" [Sil, p. 35] and of the Noldor who were students of Aule and his people it is said, "the Noldor were beloeved of Aule, and he and his people came often among them. Great became their knowledge and their skill; yet even greater was their thirst for more knowledge, and in many things they soon surpassed their teachers." [62-63]

The Noldor had the best teachers, and were the most skilled and Feanor was greatest among them. As someone mentioned, none could even understand how Feanor had crafted the Silmarills.

"The works of wonder for the glory of Arda that he might otherwise have wrought ONLY Manwe might in some measure conceieve." [112]

So generally speaking among the Elves I would say Feanor was the greatest. Someone may have mastered one art and surpassed him.