Wechat is very profitable because users use it for everything, banking, payments, ecc.
The average WhatsApp user is worth nothing in comparison even with almost twice the user base. Last time I gave WhatsApp money was the 50 cent yearly subscription when it was still an independent product.
If something has potential, it's the one that has made billions out of that potential. Unless you think that the Chinese market doesn't matter, only the Western market does.
* Wechat is used by 1.4 billion people, Whatsapp is used by 2 billion people. Clearly both apps are popular (although Whatsapp wins).
* Wechat is used by a single market, Whatsapp is used throughout the world. Clearly one has more potential than the other.