The first number refers to the amount of narcotic in the drug, the second to the amount of acetaminophen. Acetaminophen does enhance the effectiveness of the narcotic but of course it's not the main painkiller. The second one has doubled the amount of narcotic - it's the stronger one.
the 5/500 has more tylenol (500mg) and the 10/325 has more hydrocodone (10mg) I personally think the 10/325 works better for pain.
A couple of things, If the acetamenaphen is helping you better than the 5/500 would work better and if the hydrocodone is helping you better than 10/325 may be for you. everyone is different and medications react differently to different people. For me I prefer the 5/500 and taking 2 of those compaired to 2 10/325 so all depends on the problem for taking it and the person taking it.