Google is much tougher to get ranked for the long run. It's fairly easy to get ranked/indexed in Google initially. The difficult part is that after the honeymoon is over, Google makes it tough on you.

Yahoo on the other hand takes longer to get indexed however once you are there it's easier to stay there.

This is very general, but that's been my experience.

BTW, seems like a great forum. Just joined and glad I did.