The only opioids as in fully synthetics ive had are propoxyphene, tramadol (guess thats a opioid?), meperidine, and fentanyl. As for opiates ive had codeine, oxycodone, morphine, hydromorphone. I think thats it anyway thats all i can remember at the moment atleast.
Id have to say that in terms of killing pain which is what i most want fentanyl is by far the best. It's pretty euphoric as well but not as good as hydromorphone in terms of euphoria.
So it's kind of a hard one for me. Guess it's a toss up.