Heroin vs. Morphine...
Morphine is and has been the benchmark that all other opioids are compared to for almost a hundred years. That being said, Diamorphine (heroin) is very similar to morphine and is actually converted to morphine in the brain. Heroin generally produces more euphoria and an overall higher quality high. Morphine, although less euphoric, has a more rounded high and painkilling (analgesic) properities.
I personally prefer heroin over morphine because morphine makes me very drowsy and sucks the energy away from me, as well as being alot less euphoric. Morphine also has more pesky side effects. It's just not worth it, and I usually only use it when I am dopesick and have no other option. Morphine is cheaper than heroin in my area as well.
Heroin on the other hand, whilst being more euphoric and well rounded, has it's downsides. For one, heroin is usually pretty risky business. You never know what it is cut with, where it has been (up someone's ass, for instance, which happens alot more than you'd think) and how potent it is. This is because it is unregulated (tisk tisk...). On one occasion, my friend was sold a bag of sand. Luckily he was familiar with heroin and disposed of it promptly, but imagine if he was a newbie and tried to shoot it or snort it...bad news.
Another point that deserves to be looked at is the issue of dependance and addiction. Heroin is notorious for having a slightly higher addiction potenial than most any other opioid/opiate for a number of reasons. As well, the withdrawals from heroin, though similar to most other full agonist opiates, tend to be slightly worse.
Withdrawals from heroin happen alot faster, maybe even being the fastest dependance forming of all opiates/opioids. Many people I know have been casual junk users, using a few times a month, then binge on it for three days and get moderate to severe withdrawal symptoms. The bottom line is, all things considered, heroin makes people dependant on it alot faster than most other opioids/ates, and withdrawal from it is among the worst of any opioids/ates (with the exception of methadone, oxymorphone).
They are very similar (with good reason, as they are practically the same drug), and the differences are usually subtle for the most part. A mentioned above, most people wouldn't be able to tell the difference between the two if they didn't know any better. I think morphine is safer than heroin generally, but heroin is overall the better drug.
Morphine Heroin
Pros Cons Pros Cons
-Longer lasting. -More side effects -More Euphoric -Unregulated
-Regulated -Dull High -Less side effects -Socially Taboo
-Cheaper -Less Efficient -Intense Rush -Short duration
-Many Forms -Stronger Potency -Comp. Illegal