For live specimens, the 100-400 will give you a lot more reach, of course, compared to the 100 macro. It also has very close focus (to about 1:3 life size). It's excellent quality (I have one), but the macro will be a bit sharper. The latter may not be noticeable with handheld shooting.
You were right Danny, I recently purchased a Canon 100-400 mm IS II USM zoom, and it is my favorite now Our friend Antonio Giudici told me to buy an extender 1,4, but unfortunately the autofocus is not compatible with my 70D