Both systems are corrupts and amoral. but to be honest the system the tevinters use is superior. After all the chantry's system has completely collapsed on itself and thedas faces is greatest danger since the first blight.
I suppose that you mean superior only in endurance, don't you? Because there are many kinds of superior and moral superiority is certainly not in Tevinter.
Also, don't assume things before time. Tevinter's system already collapsed once, the Blight+Andraste crysis, and only survived thanks to Archon Hessarian's deep reforms. However, the Imperium is going back to their old ways little by little, and they can face collapse again, especially since their slavery system provides supporters to the Qunari invaders. If Dramatic Hands Moustache Guy is indeed the rumoured Tevinter magister, we'll have a new outlook at it.
Slavery is still in power and the system is corrupted to the core and you use it as an example of pro mage society
How lovely
Sorry, but in this I have to give the reason to DKJaigen. You said that the Circles taking the mages' children would be akin to prisons are assylums, where mothers don't keep their children "if it is decided that they can't take care of children due to their criminal past or mental health problems", and that mages "aren't allowed to have children because they are dangerous to both them and others".
However, DKJaigen pointed out that Malcom Hawke had a good mage family and that Tevinter has seen long family lines for centuries. So mages can take care of their children. If in Tevinter they teach them horrible values is another thing entirely. Normal people can teach their children horrible values too, but they are not deemed a danger to them and thus nobody takes their children.