My favorite is @merriam-webster.com. Their website is easy to use, and I really appreciate the built-in thesaurus. It makes looking up words and finding alternatives so much easier.

Discord wins thanks to its established community. i think Teams is preferred because of the integration with other Microsoft apps; after all, they license companies with all their apps. of course, that doesn't change the fact that Teams is bloatware, and that it loads endlessly.