I'd say definetly Oxy insuffilated; it gives a nice rush, and I love the taste. Makes you feel great, and gives you a nod if you want it or lets you do whatever if you don't. I'm not crazy about taking it orally, crushed or not... it just makes me sleepy (including liquid). I guess I'd say oxy is the most CONSISTENTLY euphoric opioid...
H is good too, but it varies too much in quality and cut. I've never puked from oxy (well, not by itself) but I have from H many times, and not nescessarily because of quality- sometimes it just has nasty cuts. Oxy is a more measurable drug as far as effects.
Fentanyl is great too, but if you wear it it takes wayyy too long to work, smoked is ridiculously too short, and eating the gel is most fun but I guess there's a loss of potency if you do it that way (for a while my fav. would be to eat a 10ug/hr patch and spend the day being unable to see straight). I guess it'd be a tie between oxy and fentanyl, but oxy is easier to dose and gives immediate effects.