ChaCha is a little faster and apparently a little more secure. Dig through http://www.ietf.org/mail-archive/web/tls/current/msg10843.ht... for reference.

EDIT found a better one: http://www.ietf.org/mail-archive/web/tls/current/msg10630.ht...

"ChaCha" family of ciphers aim to increase the diffusion per round while achieving the same or slightly better performance.The Aumasson et al. paper also attacks ChaCha, achieving one round less: ChaCha6 with complexity 2^140 and ChaCha7 with complexity 2^231

https://en.wikipedia.org/wiki/ChaCha20

Also used in:

https://tools.ietf.org/id/draft-agl-tls-chacha20poly1305-04....