Which is most effective; hydrocodone, fentanyl, oxycodone, or methadone?

No such thing. It is not what is most effective, it is what is best for you. I am sure your doctor will choose the safest type of opioid to treat your pain and see how you respond. If you do not respond, then he/she may try a different opioid. The most important thing is to find out what is causing a pain bad enough to require and opioid.
All different. They have different uses and modes on administration. Hydrocodone and oxycodone are taken by mouth and last about 3-4 hours. Methadone takes several hours to days for its full effect and last a very long tie. Fentanyl is available through a patch or IV and is short acting and extremely potent.

Related Questions

I have been on methadone and oxycodone for several years for knee and back injury. I just tested pos. For fentanyl. How can that be?

See a Psychiatrist. Gregg l. Friedman md, psychiatrist, agrees. Read more...
Nonspecific tests. Most drug tests do not differentiate between the opioids. The drugs that you are on could give a false-positive reading for a different narcotic, depending on the test. Read more...