What are the differences between curve NIST P-521 and Edwards E-521 for signature? I implemented and used the P-521 curve for ECDSA. Signatures are 132 bytes long.
It seems that Edwards E-521 is safer but I did not investigated very deeper.

What is its signature length ?

How is it better ?
What is its signature length ?


Depends on what algorithms you use, but with ECDSA the signature length is twice the length of the order of the base point. For P-521 that's 1042 bits, or 132 bytes when using whole bytes for each part. For E-521 it's 1038 bits or 130 bytes.


  How is it better ?


The design criteria for E-521 are stated in A note on high-security general-purpose elliptic curves:


  The curves Curve25519 and Curve1174 have been engineered to facilitate simple, efficient and secure implementation of general-purpose elliptic curve cryptosystems, with impressive results [8]. On these grounds, it makes sense to look for similar curves at higher security levels.