I do not have one favorite hymn. There are a few that are "unfavorites": Beyond the Azure Blue, I Come to the Garden Alone, and most Stamps-Baxter (which have very little praise and are often sung for the fun of rolling parts). I do love Amazing Grace, Come Thou Fount of Every Blessing, In Christ Alone, Sacred Head, and Breath of Heaven. I can tolerate most of the "old" songs (except When the Roll is Called up Yonder) like I Love to Tell the Story, Blest Be the Tie, etc.
I'll have to add that I am very interested in the history of church music, particularly that of the 18th, 19th and 20th centuries. I enjoy hearing the back stories of hymns thanks to folks like Jerry Rushford. Here are some titles of book on this subject: ABIDE WITH ME: A PHOTOGRAPHIC JOURNEY THROUGH GREAT BRITISH HYMNS by John Parker, THEN SINGS MY SOUL by Robert Morgan, A SONG IS BORN by Robert J. Taylor (this one is a little too preachy), and AMAZING GRACE by Steve Turner.
Among my favorite verses from hymns is this one from The Love of God:
vs. 3 this verse is said to have been written by a Jewish rabbi (Meir Isaac Neboria) in 1096:
"Could we with ink the ocean fill,
and were the skies of parchment made,
Were every stalk on earth a quill,
and every man a scribe by trade,
To write the love of God above
would drain the ocean day,
Nor could the scroll contain the whole
Tho' stretched from sky to sky.
Currently my favorite hymns are the contemporary praise songs adapted by The Zoe Group and particularly those sung by the director and his wife.