I would think distilled is purer... But i guess you never know what could condense with the water. Maybe nothing... R/o needs sets of filters that work less and less well over time.. so eventually... Something sneaks in there too..
Distilled water is only as good as its pre filter source & the type of source water you have. They do not work as well if you are using surface water that is hard. Trust me I own a good one 1 had to give up on it . too many issues & then there was the stainless steel tank that tasted a little funny. And yes r/o have problems also. regular filter changes are needed but run fairly consistent & do not need electricity to run. They will also beat the pulp out of even a good still in production. But given the right conditions & softer water with proper pre filters they will yield a purer water. 99.9 verse 97-99 % pure in r/o but that will depend on how good the stills pre & post filters are. Also an r/o membrane can last a long time, maybe years pending on usage.