Both are strong opioids as you know. On a MG per MG basis Opana is wayyy stronger than MS Contin (morphine) but obviously they will give you the appropriate corresponding morphine dose to opana dose. Morphine is good but for me it was too sedating and very binding when I was on it very briefly so I just stuck with hydrocodone (my doc gave me the choice of hydrocodone or morphine recently and I chose hydrocodone). Morphine is also very much "natural" which means your going to get more side effects like itchy skin, histamine response, etc. Overall I felt like it Morphine has allot more dramatic side effects compared to other opioids but you'll have to get used to it...if its too harsh I would honestly just go with oxycodone IR and deal with the taking the dose every 4 hours and what I used to do is taking a heavier dose at night so I could sleep and it would last longer...hope that helps!
PS: If you have any advice for my thread I just posted I would really appreciate it! :) really need advice with my pain :/