I've also noticed the quality of DuckDuckGo search results has been steadily improving, especially over the past year. I would encourage anyone who tried it and went back to another search engine to consider giving DuckDuckGo another shot--you may be pleasantly surprised!
In the mean time for general searches, I either use DDG's results or slap on a pre-emptive !g on a hunch, randomly or just-in-case. My idea behind this is that, as DDG's results become better, I'll habitually start using !g less and less.
And indeed, DDG's results have become better, and indeed I have been using the !g command less and less.
Google Search with !g is slowly becoming "just another one among the predefined !bang commands", a command I will append after my searches when I specifically desire to find out what Google has to say about a certain query. Though in comparison I hardly ever use !y and !b (Yahoo and Bing, respectively), mostly because I have no clue in what vague sense those results would be better (with DDG vs Google, I sort of have a feeling when asking for something really mundane and stupid, Google always hits the spot exactly, DDG sometimes misinterprets--though less so lately).
For image searching I really use !yi, !bi and !gi pretty much randomly. They all give quite different results, but as far as I've been able to determine, none of them are of particularly better quality than the others. Yahoo Image Search has a nice integration with Flickr though, so I tend to use it more when my target may be found between high-ish resolution photography.
I already named !wayback, anyone got any other cool !bang commands they use often? For instance, any good documentation searches for JS/DOM/HTML/CSS etc? I tried !mdn but I don't like their search result pages. Same for !python, if I do "!python itertools", I want to be taken straight to the itertools module documentation, not a results page of all python docs that contains the term "itertools".