Minimus,
The poster JWs made a good post from a non-Catholic perspective. I can see how the 'smoke waving' at a funeral might come across a little strange to someone with JW roots. And his comments about the Bible are mostly fair, except that the Catholic Church did not 'cherry pick' because they did not need to do so. Their liturgy, tradition, and teaching were well established for 400 years after Christ, before the Pope asked St. Jerome to compile the Apostolic letters, that eventually because the Bible. The 'Bible' as we know it was not declared inspired until the 8th century, after centuries of debate by scholars.
To answer your question ... yes, the Catholic Church and Orthodox teach the truth. They both have deep traditional roots in the primitive Catholic Church, prior to the Great Schism in 1054. Do they make mistakes, yes, but not on matters of faith and morals. They never change those long held teachings. But their ritual and liturgy, while still resembling the early Church, is something that changes from time to time ... but of itself, such practices are not what Catholics would call 'truth.' Rather, what Catholics see as 'truth' is found in what Jesus said of himself, "[He] is the Way, the Truth, and the Life." This is what I believe as a Roman Catholic.