Just wondering, which protocol, TAP or NTor is less computationally intensive for a relay to process and why ?
ntor offers reduced computational complexity for circuit setup compared to TAP. Tor circuits are setup one hop at a time with each link using TLS. Diffie-Hellman (DH) is the algorithm used for computing keys to be exchanged and is responsible for what we conceptually know as forward-secrecy.
Notable differences between TAP and ntor
Tor Authentication Protocol (TAP), the original/legacy handshake, will be used where ntor isn't supported.