OP, which DDI rifles are you talking about, the surplus parts kits or the new (PSA owned) USA made rifles?
Which parts kit rifle are you looking at and what do you want to do?
Your question is much like asking "How does Toyota compare to a Lexus LS500?" OK, which Toyota and what specific features or aesthetics do you value?
Short answer, there is no comparison, Arsenal rifles are better.
Long answer, DDI hungarian stamped are pretty good, DDI forged bulgarian milled are ok, DDI/PSA USA made are probably low value when compared with WASR (cheaper/better) or Arsenal stamped (way better) or milled (way better/more expensive).
DDI had kg guncote finishes, decent barrels, and decent assembly. Sights are pretty straight and fair attention to detail.
If you want a trunk gun and are worried about rust, DDI would be great. Do you want a bayonet? DDI milled bulgarian sucks ass, but hungarian is great.
etc.