Here's my top ten list. To me "hymns" means older songs, usually with at least four verses sung only once each, and usually found in hymnals. Shorter, newer songs that are often sung more than once and often appear on overheads I call choruses or worship songs - are you looking for favourite choruses as well?

Holy Holy Holy
Great Is Thy Faithfulness
Praise My Soul the King of Heaven
Be Thou My Vision
O God Our Help in Ages Past
Joyful Joyful
Advent: O Come O Come Emmanuel
Christmas: O Come All Ye Faithful
Good Friday: O Sacred Head
Easter: Crown Him With Many Crowns
Pentecost: The Church's One Foundation

Marion