is more stimulating and more euphoric, but much shorter-acting than morphine
is similar in euphoria
and soporific effects, but lasts considerably longer. Both oxy- and hydrocodone are significantly more bioavailable than morphine when taken orally - oral use of morphine is highly inefficient, compared to other commonly used opiates
(I believe around 20% makes it to the bloodstream). Oral preparations of morphine come as salts, so they must be converted to freebase for smoking. Oxycodone and hydrocodone also come as salts, but they are relatively efficient for oral use, so there's less reason to freebase them.
Morphine is most comparable in "high" and painkilling to codeine
- codeine is not itself psychoactive
- it is converted by the liver into active opiates, the main one being morphine. Morphine does tend to be tolerated better than codeine, with less allergic reactions and sub-allergic histamine problems (itching/rashes, etc). Also, only a certain amount of codeine can be handled by the liver at one time, so doses much over 400mg tend to be less and less effective. Morphine is also very similar to heroin
- heroin is converted in the brain to morphine, and it is actually a morphine high that heroin users experience, but the structure of heroin gives it a much higher affinity for crossing the blood-brain barrier, meaning it hits harder and faster than morphine that hasn't been diacetylated.
Hope that helps!