Has anyone checked if Wiktionary's quality is good?
In my experience, Oxford dictionary are better than Meriam-Webster's dictionary.
My favorite professional editor tells me that in general, for English definitions and usage, MW is preferred to the OED. OED is generally better if you care specifically about etymology, but otherwise, MW has the edge for usage, especially modern usage, as the OED is (deliberately) slower to add words and update usages.
This is, of course, a very broad comparison, and both are good enough for most people.
Hope that helps,
~Chad