Regarding the UI, I guess it is a matter of personal preference, although in lichess you have all the time controls in the front page, one click away, while chess-dot-com only has 10 min games in the front page, and for any other time control you need several more clicks.

Lichess has unlimited puzzles, which is a huge plus (although it also a huge temptation for procrastination).

chess-dot-com has better educational material, although nowadays there is lots and lots of high quality material elsewhere.

I really like lichess’ open source model. But to be fair, chess-dot-com re-invest a lot in supporting tournaments and content creators, so they are also a force for good in the community.

At the end of the day, they aren’t mutually exclusive. You can use both of them for different things.