The difference btwn strong opiates are less than the difference btwn our different body chemicals, if we shoot it/eat it/snort it, if we take it when we are tired, happy, sad etc. Etorphin is many times stronger than heroin, as is fentanyl, but that does not mean that the euphoria is greater, only that you need less.
Longtime junkies like myself (had my first shot 1974) have always had to use pharmaceuticals when the H is bad or scarse. But when heroin is good and plentiful ppl tend to prefer that over all other stuff. I am of course talking about i.v. use. I know that many in England was said to actually prefer Diconal to heroin, and I myself would perhaps prefer Ketobemidon if it wasn't so wildly addictive and the WD so agonizing. But otherwise heroin rules.
I have never tried oxymorphon or levorphanol, but almost all other stuff several times, and my opinion is that Heroin is number one among almost all junkies that I know. Hydromorphone gives a wonderful high for a couple of minutes after the shot, but after that the euphoria is not as good as morphine. I have never met anyone who actually prefer fentanyl to i.v. heroin. Methadone and meperidene - or pethidin as we say in Europe - are underrated; they are good when you shoot'em. Only times I take codeine is when I am sick and cannot get anything else - luckily that isn't very often. Oxycodone is much better than codeine but not as good as morphine. Tramadol isn't even worth mentioning.