It depends! I am a volunteer Destination Expert with Tripadvisor.com. In the forum where i operate, namely Portugal, there is a lot of activity and many contributors with excellent knowledge who are frequently able to provide comprehensive replies to answers.
However, there are other forums, (e.g. Romania, Seville etc) where there are fewer contributors and destination experts and where the quality of the knowledge available is much less comprehensive or useful.
One should check out the forum for the country in question to see whether one feels that a Tripadvisor.com forum for a specific destination is comprehensive enough. Then decide whether to post there or on quora.com.
Be aware that Quora.com is not a travel info website so may not be sufficiently specialised for responses to travel questions
