Mom, if you're talking a.m. cardio on an empty stomach I'm pretty sure that coffee should be black - the goal being the caffeine will help with fat burning / metabolism and you're still in a fasting state, helping with the production of HGH (human growth hormone). If you're talking resistance workouts then I don't think it's as big a deal; frankly I've done a.m. lifting workouts and p.m. lifting workouts and I greatly prefer the latter ( I am a lot stronger and more focusses with some food in me).

All I can suggest is try it both ways and see if you notice a difference over the course of a few weeks.

Cheers,
Nat