Favorite scream in rock?

Thys Van Leer from the Dutch prog band, Focus.

He does not usually scream, but on their song, "Hocus Pocus", he screams at the end of some impressive yodeling.

https://www.youtube.com/watch?v=g4ouPGGLI6Q

On a side note, even though this song is pretty fun, it is kind of sad that this is what they are remembered for, since they have a catalog filled with great prog songs.

The Beatles, “A Day In the Life”, when I forgot which Beatle screamed ‘I got blisters on my fingers.”

Any song that Steven Tylor from Aerosmith screams in.  Also, we can’t forget Rob Tyner from the MC5 when he screamed “Kick out the jams motherf*****.”

John Lennon on She wants you (she’s so heavy) on Abbey Road.

My Woman From Tokyo by Deep Purple

Lead vocalist from Swedish progressive-metal band, Pain of Salvation, Daniel Gildenlow, has many great screams throughput the band's catalog, it's hard to narrow it to one. 

He also has amazing vocal chops overall. He has a 5 octave range, great intonation, ability to sing quiet in a pure voice, power to spare. 

At about the 4:27 mark on the song, "Used", is one example. 

At about the 3:40 mark of the song, "Handful of Nothing.

Another example is a live version of the song, "Hallelujah" at about the  7:40 mark. 

"Nobody screams/sings like Eric Adams - no, not the NY Mayor..."

Not so fast, he may be screaming real soon...

Lots of great ones mentioned. A couple of others

Geoff Tate - Queen of the Ryche

Ronnie James Dio - The last in line

The Metal God himself.  Rob Halford.  Full Stop.

Nobody screams/sings like Eric Adams - no, not the NY Mayor, but the singer in Manowar over the past 4 decades or so.... 

Alice Cooper screaming "Wake Up - Wake Up" towards the end of "Black Juju".

DeKay

Roger Daltrey in "Won't Get Fooled Again"

Paul McCartney "Monkberry Moon Delight"

Roger Waters (Pink Floyd) "Careful With That Axe Eugene"

Beth Hart - Whole Lotta Love. 

Led Zeppelin-Whole Lotta Love

Jim Morrison When the Musics over from Live at the Hollywood Bowl, at the 10 minute mark: We want the world and we want it Nowwwwwww:

The Doors - Live at the Hollywood Bowl - July 5th, 1968 - Full Concert

Chris Cornell 

Gotta go with, Supertramp's School.  For someone who is not familiar with the song and you crank it up, it will make you jump in your seat.  -John

Aerosmith - Dream On - Steven Tyler

James Brown hands down...no contest. The scream master!

Second place to Ian Gillan as Jesus and in many a Deep Purple tune: "Perfect Strangers" for example. James LeBrie with Dream Theater did a very impressive cover on their "A Change of Seasons" record.

Tina Turner in her early days with Ike no slouch either.

Howard Dean

Kala Rose covering Black Label Society's "Crazy Horse":

https://www.youtube.com/watch?v=oYEXeW94z5A

Roger Daltrey-"Won't Get Fooled Again."

Pink Floyd. Another Brick in the Wall, Part 2. 

...said to be influential in the development of Roger Water political philosophy..

fairly innocuous at the time, but Roger would continue to become obsessed with his political philosophies..as anyone who has been to a concert of his in the past 10 years can attest!

James Brown.

Arthur Brown, Fire is it for me.  

Supertramp's School

Jim Morrison.

Several by David Lee Roth in Runnin’ With the Devil.  Very close second is DLR in second verse of Outta Love.  Maynard at the end of Eulogy.  Sorry I know you asked for one but there are so many.