It is not a good idea to take them together because Advil (ibuprofen) is a non-steriodal anti-inflammatory drug pain reliever and Excedrin is also a pain reliever that contains acetaminophen, aspirin and caffeine. These two drugs taken together have what's called a major drug interaction, something to do with aspirin and ibuprofen and blood clotting issues. However, most all NSAIDs work the same, so you can choose one and maximize your use within the perimeters on the bottle.
There is good news, there are now over 100 medications and supplements that can be used for Migraine and headache prevention. The frustration of trying to find what works for us can make it seem as if we've tried it all, but with so many possible preventives, it's literally impossible to have tried them all. See Migraine preventive medications - too many options to give up! for more information.
You should not take Advil and Excedrin together because the Excedrin contains Aspirin which is an NSAID, Advil is also an NSAID, taking these in excess can cause damage to your kidneys.