Melody A is more sad... It's a unique mix of sadness and joyfulness. This psalm was composed by David, who had to leave Jerusalem and had to run for his life because of his son Absalom's persecution. And when Absalom was killed, David was extremely sad. He wished that he himself would die instead of Absalom. And then... he went back to Jerusalem, to the house of the Lord and sadness was turned into happiness. And so will it be also with all of them, who will come into heavenly Jerusalem, Sion. They will be sad because of so much evil, which they have seen and experienced in their life and because their loved ones have rather chosen evil than good (lie - truth, evil - love, death - life, Devil - God...) They rather perish than to come to our Saviour, Lord Jesus Christ. But after that, the God's children will be comforted and joyfulness will enter and fill their hearts for ever and ever... Bless be the Lord.
And in melody B there is practically no sadness (I hope:) To Jews, who were in exile in Babylon, was said, that they will return to Jerusalem... And there was so much happiness... I guess they even cried out of happiness and so will it be with people, who will come in the city, heavenly Sion... Praised be the Lord. And even we, when only thinking about those things, are crying out of pure joy. Bless be the Lord and his mercy - He has forgiven us our sins and is forgiving us daily and is sanctifying and changing us, our hearts and minds day by day... Yes, Christianity does work - the Gospel is the power of God. We are strangers in this world and we are pilgrims, who are going to the most sacred and holy place of them all (well, to the only sacred and holy place) - before his presence, toward our home :) Our life on this Earth is the pilgrimage for us... That is the meaning of life... To know Him, to come to Him, to glorify Him and to make Him happy, to be grateful to Him, because of everything He did for us... Praised be the Lord :)