Some older songs contain false teaching (I once was lost in sin . . . but just a little talk with Jesus made it right”. Others have figures meaningless to many (Night with ebon pinion, “Here I raise my Ebenezer, Let the lower lights be burning”). Other lyrics are more doggerel than poetry and sometimes the music is unsuited to the words.
While many of the newer songs are “praise” songs, older songs are often more suited for “teaching and admonishing one another” (Col. 3:16). Many cherished hymns are sublime in words and music. (When I survey the Wondrous cross”, More holiness Give Me”, “It is well with my Soul”).
Some new songs deserve the appellation, 7/11 songs: “seven words repeated 11 times.” Others have uneven rhythms and unconventional note patterns that are difficult to learn and sing.
However, many teach relevant, Biblical truths beautifully (In Christ Alone” “Ancient Words”. Often they are Biblical passages set to suitable music “Great is Thy Faithfulness” “I am Crucified with Christ”.
Rather than choose between “new or old”, choose the best of both. Seek a carefully thought out balance of good songs, both old and new.