O Sweet!

First I discovered Chess.com.
Second, I discovered Lichess.org, and I liked the slimmer, cleaner, smoother feel of it.

Over the past few months of playing on both platforms, I have to say I am pretty heavily leaning toward Lichess as the favorite, and may convert fully and abandon Chess.com completely (and cancel my paid subscription!).

Lichess has shown to be far more stable in my experience, where "the other guy" frequently crashes or gives me "system unavailable, try again later" messages after I'd just successfully solved a difficult puzzle and now gotten no credit for it.

The Lichess app doesn't have all the features of the website yet, but enough that it's great in my pocket as well.