OpenSSH since 5.7 prefers ECDSA over RSA and DSA keys, but you may get errors such as:
Error calculating host key fingerprint. ... The fingerprint for the ECDSA key sent by the remote host is ... Offending RSA key in /home/troll/.ssh/known_hosts:10 ...
There seems to be no way to use the old RSA public key in you
known_hosts to automatically trust the new ECDSA key. You'll have
to either copy
/etc/ssh/ssh_host_ecdsa_key.pub into your
known_hosts file by hand, or do the usual
See Phil Pennock's (the Grumpy Troll) post for more details