If you're working with two SSH keys (work / personal) then the following setup is quite elegant. It assumes all repositories are work related, unless they're hosted under your own user:
Host *
AddKeysToAgent yes
UseKeychain yes
StrictHostKeyChecking no
User git
IdentityFile ~/.ssh/id_rsa_corporate
# personal account
Host github.com-MYUSERNAME
HostName github.com
User git
IdentityFile ~/.ssh/id_rsa