Note that "!r <foo>" is different than "site:reddit.com <foo>". The former redirects you to reddit's own search, the latter keeps you on DDG but restricts the results to reddit.com.

I prefer "site:reddit.com" but honestly it's only because I'm used to it. I search in-app on mobile frequently (which I assume is the same as the on-site search) and it's generally pretty good. It usually finds something for me but sometimes using an external search engine works better.