Ive banged countless fentanyl patches and actiq, in doses up to two 100ug/hr patches simultaneously. The rush is good, no doubt, but it doesnt last at all. 30 minutes later and you are sober. Same thing with the sublimaze fentanyl citrate ampules, they have a good rush, but simply do NOT last. And yes, ive tried oxymorphone suppositories and IV, but again, nice rush, lasts longer than fentanyl, but still not that long. I have injected alpha-methylfentanyl, carfentanil and sufentanil, and again, all of these are GREAT drugs, but they simply dont last long enough. Its like opioid crack, you are left fiending for another hit. I suppose if you had unlimited supply, it would be a great drug. And yes, smoking fentanyl does provide a suprisingly strong rush.....
But from all the stuff IV banged, I like drugs like levorphanol, which may not have that extreme ear-ringing rush of fentanyl analogues, but has a nice long lasting high. Other good examples of good injectables are ketogan (ketobemidone), and dipipanone (aka diconal, which is dipipanone and cyclizine, the holy grail of some european addicts).
But I have to say, I really am fond of good old diacetylmorphine (or 6-mam), as heroin both has a good rush, and comparatively, it lasts long. I take my half-gram shot at night (along with a lot of diazepam) and i sleep like a baby, which is the only thing that I have found that really overpowers my persistant insomnia. Heroin is popular for a reason, it is good shit....