Top 10 Singers from Whose Vocal Technique One Can Learn the Most (Excluding Opera Singers)

The items in this list have been selected by the author of the list for you to vote and comment on.
The Top Ten
1 Freddie Mercury Freddie Mercury (born Farrokh Bulsara, 5th September 1946 - 24th November 1991) was a Zanzibari-born British singer of Indian descent, songwriter and record producer, known as the lead vocalist and songwriter of the British rock band Queen. He also became known for his flamboyant stage persona and four-octave vocal range. Before he became a singer he has been in 3 other bands (Ibex, Sour Milk Sea, and The Hectics). He died on November 24, 1991 from bronchopneumonia as a result from HIV/AIDS

Obvious one.

2 Dimash Kudaibergen Dinmukhamed Kanatuly Kudaibergenov, commonly known as Dimash Kudaibergen (born May 24th, 1994) is a Kazakh singer, songwriter and multi-instrumentalist. Dimash is best known as a contestant of Chinese talent show "Singer 2017" where he was declared a runner-up. He is also known for possessing a wide vocal range, measuring up to 5 octaves.

I added him after I made this list because I wasn't familiar with his singing. But now I am and...wow!
A vocal coach said, "If you want to have a great example of what a perfect vocal technician is, listen to some Dimash ‘cause he’s amazing." - Tara Simon (in: Vocal Coach Reacts to Dimash Kudaibergen - Love is Like a Dream).
After hearing a song by him, another vocal coach wanted to buy a flight ticket to Kazakhstan and receive training by him (though such master class isn't available).
Check out my list - Top 10 Quotes From Vocal Coach Reactions To Dimash Kudaibergen Vocal Performances

Every vocal coach who reacts to Dimash’s songs always ends up a diehard fan. His technique flawless, his vocal range is insane, and he can transition effortlessly from different styles in just one song.

3 Rob Halford Robert John Arthur "Rob" Halford is an English singer and songwriter, who is best known as the lead vocalist for the Grammy Award-winning heavy metal band Judas Priest and famed for his powerful wide ranging operatic voice.
4 Ian Gillan Ian Gillan is an English singer and songwriter. He originally found success as the lead singer and lyricist for Deep Purple, and the original singer on the rock opera concept album Jesus Christ Superstar by Andrew Lloyd Webber, where Gillan had the leading role (Jesus Christ).

Bruce Dickinson of Iron Maiden learned from him.
Hansi Kürsch of Blind Guardian also admitted that - I think Hansi's systematic screams in Tanelorn Into the Void are inspired by Gillan's systematic screams in Hard Lovin' Man by Deep Purple.

My vibrato is a mix of his, Dio's, and Dickinsons. I tryed to extend my range mostly because of him.

5 Geoff Tate Geoff Tate is a German-born American singer and musician who rose to fame in the 1980s with the progressive metal band Queensrÿche.

He used to take singing lessons in his younger years and his vocal technique became almost flawless.

6 Hansi Kürsch Hansi Kürsch, born Hans Jürgen Kürsch, is the lead singer, lyricist, co-composer and bassist for German power metal band Blind Guardian . Heavily influenced by Freddie Mercury, he creates a huge choir effect by overdubbing his own voice multiple times in complex, overlapping vocal harmonies. He records each vocal track individually because harmonizers and "perfect pitch" programs don't work with his voice due to distortion and the natural double layer effects his vocal cords have .
His early technique made use of a more aggressive and harsher, "screaming" technique . ...read more.

"During the performance of a 'clean falsetto' air stream runs up the spine and finds an almost straight way out to my nostrils. My jaw region is relaxed; I could even chew gum." - Hansi Kürsch
(even though he rarely uses falsetto, he knows how to do it)
What impresses me the most is his switching and his belting. He switches all the time and does it effortlessly. His belting is extremely powerful (besides, not every singer can belt but he can).

7 Ronnie James Dio Ronnie James Dio (born Ronald James Padavona; July 10, 1942 – May 16, 2010) was an American heavy metal singer, songwriter and musician. He fronted and/or founded numerous groups including Elf, Rainbow, Black Sabbath, Dio and Heaven & Hell. He is credited with popularizing the "metal horns" hand gesture in metal culture and is known for his medieval themed lyrics. Dio possessed a powerful versatile vocal range capable of singing both hard rock and lighter ballads; according to Rainbow/Deep Purple guitarist Ritchie Blackmore upon hearing him sing, "I felt shivers down my spine." Dio sold over 47 million albums throughout his career. He died from stomach cancer in 2010 at the age of 67.

Everything he did was pure gold.

8 Tobias Sammet Tobias Sammet is a German metal musician, best known as the vocalist and primary songwriter of the power metal band Edguy, as well as the founder, main singer and bassist of the metal opera Avantasia.

He usually sings with a very relaxed larynx and this results in gorgeous sounds (Edguy - Sacrifice, 5:05-6:05; Nailed to the Wheel - intro vox).

9 Marc Martel
10 Layne Staley Layne Thomas Staley was an American musician who served as the lead singer and co-songwriter of the rock band Alice in Chains, which he founded with guitarist Jerry Cantrell in Seattle, Washington in 1987. Alice in Chains rose to international fame as part of the grunge movement of the early 1990s. ...read more.
The Contenders
11 Whitney Houston Whitney Elizabeth Houston (August 9, 1963 – February 11, 2012) was an American singer, actress, producer, and model. In 2009, Guinness World Records cited her as the most awarded female act of all time. Houston is one of pop music's best-selling music artists of all-time, with an estimated 170–200 ...read more.
12 Christina Aguilera Christina María Aguilera is an American singer, songwriter, and record producer, best known for songs such as "Beautiful", "Genie In A Bottle", "Fighter", "Hurt", "Dirrty", "Your Body", "Lady Marmalade", "Reflection", "I Turn To You", "Come On Over Baby (All I Want Is You)" "What A Girl Wants", and ...read more.
13 Michael Bolton Michael Bolotin, known professionally as Michael Bolton, is an American singer and songwriter. Bolton originally performed in the hard rock and heavy metal genres from the mid-1970s to the mid-1980s, both on his early solo albums and those he recorded as the frontman of the band Blackjack.
14 Bruce Dickinson Paul Bruce Dickinson, known professionally as Bruce Dickinson, (born 7 August 1958) is an English musician, airline pilot, and broadcaster. He is most well known for being the lead singer in heavy metal band Iron Maiden and his solo career.Outside his career in music, Dickinson has pursued a number ...read more.
15 Steve Perry Stephen Ray "Steve" Perry is an American singer, songwriter, and record producer. He is known as the lead singer of the rock band Journey during their most commercially successful periods from 1977 to 1987 and again from 1995 to 1998.
16 Tim Buckley Timothy Charles "Tim" Buckley III (February 14, 1947 – June 29, 1975) was an American singer-songwriter and guitarist. His music and style changed considerably through the years; he began his career based in folk music, but his subsequent albums incorporated jazz, psychedelia, funk, soul, avant-garde ...read more.