I currently use both. On chess.com I mainly play daily games, do my daily 5 free puzzles and 1 free puzzle rush, and on lichess I play rapid, blitz and bullet, do unlimited free puzzles and take part in tournaments, of which some are rating-restricted (e.g. <2000 or <1500) On lichess there are a bunch of user- made educative studies, also lichess's own educational resources on all kinds of tactigues and checkmate patterns. Lichess has free game analysis also, to see where you went wrong. Overall, both websites offer a good range of features, but my honest opinion is that chess.com's popularity is largely due to its domain name, which makes it sound official. I think that if the names were switched, the current chess.com business-centered format would be far less popular than lichess's open-source community-centered format.
Main difference is how elo is calculated and paywalls.
Lichess.org has no paywalls and it is difficult to increase your elo the higher you go.
Chess.com on the other hand makes you pay for most of the important stuff and has harder lower elos than Lichess.
In fact lichess is probably more beginner friendly and less competitive in my personal opinion. Chess.com on the other hand is hard for beginners unless you've got money to burn.
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