I think the other two "mainstream" messengers I use (Telegram, KakaoTalk) are as simple or simpler and also ad-free. Kakao also has E2E encryption after a bit of a struggle, Telegram had it for a long time.
I think WA is the most widespread but I wouldn't call it the simplest or most reliable. They are all pretty similar imo
I think WA is the most widespread but I wouldn't call it the simplest or most reliable. They are all pretty similar imo