Well you're asking two separate questions. As 1mg=1000mcg and fentanyl is dosed typically around 50mcg, whereas dilaudid's starting dose is around 2mg, and oxycodone's at 5mg, clearly fentanyl mg for mg is the most potent. And as deos68 said the quality of the high depends on ROA. IMO dilaudid IV has the strongest high at standard dosing, followed by fentanyl IV, then oxycodone orally (though the insufflated rush beats oral dosing). Everyone has their own preferences though and many factors contribute to the absorption and metabolism of each drug.