Joel
I did allot of research when I bought mine, and opted for the 24ex. I haven't used the 14ex but most of the complaints I remember reading were that it tended to make your subject feel flat because the light is direct and head on.
The complaints about the 24ex are that it is a harsh light, and indeed it is. I bought diffuser for mine. One of the advantages I see in the 24ex is that it gives you more control, both in the flash itself and the ability to adjust, move and remove the heads independently to different locations.
But, my advice for you is that while you would probably make use of either flash, you are well suited with your gear to jump in to macro without either one. With all of your back yard bird gear and off camera flashes I think you have a good equipment foundation to start with. Of course this is just like birding and wildlife; I know we both probably have our eye set on the 500mm II when it comes out.
Rick
Edit: or 600mm II