J S.

On the one hand, it's Merriam-Webster, the big name in dictionaries. On the other hand, the online version of the dictionary is so packed with ads--many of which feature audio/video that starts automatically--that it can be a chore to get to the definition you're looking for. Add to this the following additional hurdles: (1) after typing in a search word, you have to click through an ADDITIONAL page of advertising to get to the definition; (2) getting definitions to some less-common words requires membership to some higher (presumably paid) level of membership. Bear in mind, I am a professional editor and I have (presumably) a greater interest in and need for a service like M-W Online, and the site taxes my patience.