To discuss BTC, you can check out Reddit and Bitcoin Forum as mentioned before.
And to discuss LTC and DOGE, you can also check out Reddit as well as their own forums.
I. Best 2 sites for you to discuss LTC
/r/litecoin" subreddit is the main place for you to discuss Litecoin, and you can also find more places by searching for "litecoin".
LitecoinTalk is the official Litecoin forum, on which you can discuss anything about LTC in your local languages.
II. Best 2 sites for you to discuss DOGE
/r/dogecoin" subreddit has more than 20,000 subscribers (rich shibes) now, and there are over 14,000 topics about DOGE on reddit.
Like BTC's and Litecoin's, the DOGE's official forum is also available for you to discuss anything about Dogecoin in your local languages.
But there are boring Google Adsense ads and the design of black background with yellow text is boring, too.
As what you can see from the above, the best places for you to discuss LTC and DOGE are the Reddit site as well as their official forums, same as BTC.