So long as it hasn't been terribly abused or neglected, I'd expect a '99 CBR to be a good starter bike as well. If you can pick it up a good bit cheaper than the '04 Yamaha then it might be just the ticket. Money aside, sit on them both and see how they feel. Yamaha and Honda engineers have different ideas about what makes a good riding position on a sportbike. One may fit your idea better than the other.

For a first bike you want to be comfortable as much as possible to inspire confidence and ensure that you are having fun. If the machine is a torture rack or too twitchy and nervous, you won't get comfortable and you'll enjoy riding a lot less.