Is acetone or isopropyl alcohol better for removing rosin flux?
Acetone being used to clean circuit boards can be problematic. The biggest issue that I found was that it leaves a residue in the board that still requires several other cleaning steps to get rid of including IPA and hot water. 

Even IPA can leave a residue as it dries.

There is also the problem mentioned in the comments that the acetone can dissolve certain plastics to the great detriment of your electronics assembly. I've seen it eat away the plastic winding wraps on small transformers as an example.