In my experience, being a DDG user for several years, I use search to find answers to some problem I'm facing. If I can find it, I'm happy, without caring about if Google would have given me better results. I don't spend my time comparing between the two.
Based on the above, I'm been mostly satisfied, I'll say 99% of the time. In the 1% of cases where DDG has not provided me an answer to my problem, as a hail mary I try !g (Google) and sometime I get an answer and many times not.
So, IMO the difference in search for most practical uses is minor. Now, add the uncluttered user interface on top of it, DDG wins by a huge margin.
Edit: Anecdata, an area where I've found that Google is slightly better, as in having a few more results, is in returning results from forums and sometimes Reddit. But even then, DDG results are mostly sufficient and there are only a very few instances where I've had to do !g.