It's free (freedom & beer), it has no ads, and it's feature-complete. It even has stuff that other websites make you pay for, like post-game computer annotation. It offers a web interface where you can play without even registering an account and free (again, freedom & beer) apps for iOS and Android.
The only downside when compared to chess.com is that fewer top-level professionals play there. Which is not an issue unless you're literally a super GM.
It doesn't matter what connection I'm on, and the website is always instant, but the Android app always takes half a second to load any screen. It's infuriating when you want to view the analysis, or just navigate around the app.
My bug is about Puzzle Storm. When you run out of time, the GUI shows you the post game screen and it takes a fraction of a second before it pops in a "daily record" banner. This fraction of a second is slow enough for me to drag my mouse cursor over the "Failed puzzles" filter, but fast enough for me to accidentally click "Play again" as it has been pushed down the page (by the daily record div) without me perceiving it yet. Once clicked, that button resets the page to start another puzzle storm and by then I've lost the failed puzzle history, so I can't go over it anymore.
It has happened already in the hundreds of times. I can't help it, hopefully the dev one day figures it out.
It must be one of the best examples of a very large scale implementation of features that are simple and easy to understand
Also puzzles are slightly better on chesscom and (arguably) the analysis interface imo
You also have unlimited free puzzles on lichess (paid on chesscom). Chess.com probably has a better library of learning content if you're into that (much of it paid though).
IMO if you're not paying I can't see why anyone would prefer chess.com over lichess: you get less and also get ass for the trouble. If you don't care about the monthly subscription cost, then maybe chess.com has fringe benefits over lichess.
1. Lichess rating is ~200-300 points ahead of a Chess.com rating. Not in the sense that players are better, but an 800 player on Chess.com will probably be 1000-1100 on Lichess.
2. Fantastic analysis tool. Chess.com analysis tends to be a bit funky sometimes.
3. Zen Mode. Not really a pro / con, but it's nice to hide the UI and just have a board on the screen when playing.
4. Free, obviously. No ads.
5. Younger audiences may want to play where their favorite streamer players, which tends to be Chess.com for nearly everyone unless you're Eric Rosen. Hikaru Nakamura, GothamChess, Magnus Carlsen, Botez Sisters, Anna Cramling, and Chessbrah are all on Chess.com.
6. Chess.com has better puzzles, although limited on the free tier.
I don't have exact numbers on population for both platforms, but if someone can correct me, I'm fairly sure Chess.com holds the majority of players.
Maia is great, probably more human than the chess.com bots.
I also like Lichess because I can play in arena tournaments against players with a much higher rating than me, which helps me learn - I'm not sure if this is so easy to do on Chess.com.
I paid for Chess.com for a while, but I stopped subscribing when I realized I never used it. Meanwhile I have multiple days of playtime on Lichess. Also, the owners of Chess.com don't seem like very nice people.
I'm pretty sure the pros and streamers prefer Lichess too, but they're sponsored by Chess.com so they have to pretend to like it.
If your goal, however, is to popularise the game of chess, i.e. to get more people to play chess, a free online service is only a necessary condition. Chess.com seems to be able to sponsor and organise tournaments, pay content creators/chess players, offer live streams with professional commentators, etc. But also take legal responsibility and stand up to lawsuits.
Interested to hear your thoughts on this. I don't see Lichess being able to provide this type of value, and I'm not sure if they want to or should.
That said, I prefer lichess and think most people should be using it. But I understand it’s not about the platform’s technical features; for most people, it’s about the network effect with their friends.