I've got both but I got the 580EX first. Fill in flash especially with portraits was something I never did until I got the 580EX. It's great to brighten up the shadows in faces and bring out subtle details in expressions. Having a powerful flash with bounce capabilities and a built in diffuser is great to open all sorts of creative options.


Then I got the 100 2.8 macro to zoom in on flowers and insects. No bug or flower in the garden is safe and the results from the lens is outstanding. Then I decided to shoot bugs and flowers with the 100 2.8 macro and the 580EX deflector to bring out subtle details in flowers and insects. And the combination works great together!


Best advice I can give you is to decide on what you want to do first, get the first item, and when you can afford the second item, get that too.