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

#ssh