Sam Cooke is the absolute king and if there is a prince it is Otis Redding.
My personal favorite soul recording of all time is Otis' posthumous album: "Remember Me". It contains alternate recordings of many of his classics. The alternate records just blow away the commercial ones. Otis liked to do 4 or 5 takes of a song with varying degrees of soul. The people making this compilation tried to use the most "soulful" versions of a song. Right off the top of my head I can say that he has 4 of my top 10 favorite songs of all time of any artist, all on one CD:
-Remember Me
-Send Me Some Lovin (much slower than the commercially released version)
-Come to Me (the piano and guitar on this track are amazing, definitely my go to sad song.)
On all three of these, you really get the feeling that he was singing to an old lover and that his heart actually felt the pain conveyed in the songs.
-The Dock of the Bay (on this take, he actually makes the seagull and ocean sounds that were digitally put in to the real version of the song later. It is FAR superior to the commercially released track but was not released because he messed up the whistle part.)
Link to my favorite album of all time. Before I bought this I hadn't bought a CD in 3 years.
Try a Little Tenderness
My favorite Sam Cooke Song- Tennessee Waltz