Chess.com or Lichess

Lichess:  
Free and ad-free: Lichess is entirely free and ad-free, supported by donations.  
Open source: Lichess is open-source, meaning you can see and contribute to the code, ensuring transparency and community involvement.  
Focus on analysis: Lichess excels at game analysis and studying, offering unlimited free game analysis, unlimited puzzles, and more.  
Good anti-cheating: Lichess is known for having a robust anti-cheating system.  
Simpler interface: Some users prefer Lichess's clean and simple interface, which some find less cluttered than Chess.com's.  
Chess.com:  
Larger player base:
Chess.com boasts a larger player base, offering more opportunities for finding opponents and joining communities.  
More social features:
Chess.com has a wider range of social features, such as clubs, tournaments, and more customizable profiles, according to a user on Reddit.  
Chess.com's lessons:
Chess.com offers a variety of learning resources, including videos, lessons, and interactive tutorials.  
ChessKid:
Chess.com offers ChessKid, a platform specifically designed for younger players.  
More user-friendly interface:
Some users find Chess.com's interface more user-friendly, with features like profile pictures and flags. 

Lichess for analysis and chess.com for 30 minutes rapid game above 1800 rapid