While I do not know enough about Arab slavery to speak about it, the Roman institution of slavery was quite different than the chattel slavery practiced in the American South. Saying whether or not slaves were treated better or worse in Rome is a bit difficult to say. Certain types of slaves almost certainly enjoyed a rather nice lifestyle compared to those in the American South, those that toiled in Rome's mines were likely much worse off.

One key difference is that Roman slavery had virtually nothing to do with race. Slaves could come from Syria, Judea, Gaul, Hispania, Africa, Greece etc. If you found yourself on the losing side of a war with Rome, you could count on a lot of your people becoming slaves. So while slaves in the American South had to deal with racism on top of being "owned" by another human being, slaves in Rome were fortunate in that regard.

Now, while most slaves in Rome probably lived a miserable existence as agricultural laborers or miners, many important societal roles that required a high degree of training were filled by slaves. Slaves could be physicians, teachers, secretaries and accountants. Many of these slaves were actually owned by the State rather than any individual person. Moreover, many important craftsmen were likewise slaves. Most notably from Greece. Indeed the effect of the influx of Greek slaves on the cultural evolution of the Late Republic and Early Empire is very frequently discussed by historians. Many of the marble statutes, busts, monuments and architectural feats we associate with Rome can be credited to this slaves. Greek slaves also played an important role in the Roman educational system.

The owning of slaves was also an important status symbol for the upper class. Accordingly, one's slaves became an ostentatious display of wealth. The greater number of slaves one had, the more impressive. There was a "Keeping up with the Jones" element to it as well. Wealthy Roman elites would not be caught dead in public without a sufficiently large entourage of slaves. The bigger the entourage and the more "exotic" the slaves, the more impressive. The satirist Juvenal made the practice a frequent target and quipped that a Roman citizen in the middle of a court case could almost be assured of the jury finding against him if he showed up to the proceedings without at least 8 slaves in his entourage.

Many wealthy Romans thus had slaves that solely preformed a ludicrously specific job. If you were a wealthy Roman, you might have one slave to take your shoes off in the evening, one to dress you in the morning with different slave to undress you later. If one of your friends was hosting a dinner party, they might have one slave to open the door for their guests, another to show them to their seat while yet another pulled back their chair for them. The slaves that brought out the plates were different from the ones that took them away.

Flaunting your wealth through your slaves eventually somewhat humorously evolved into the practice of releasing large number of slaves to show that you were wealthy to be able to afford it. Slaves were so critical to the running of the state that this practice became a cause of concern. As a result, Augustus was forced to limit the number of slaves a master could release at one time as well as completely outlawing the freeing of slaves younger than 30.