This question is a tough one since for me it depends on the genre of music and also whether it is male or female. That being said, I can say that one of my favored singers is Tony Bennett - at 80 years old he still sounds just about as good as he did back in the early parts of his career. My almost two year old like him too so he must be good.
I ask her do you want to listen to some music and the first one chosen is often "Tony Bennett".
I'm listening to the group Avalon right now while I write this and I am impressed with their sound, I do agree with the choice of Freddy Mercury. I remember seeing a bit on him singing with Placido Domingo and all I could say was WOW!
I also enjoy Nichole Nordeman, Joy Williams, Jaime Jamgochian when she sings the song "Hear My Worship". That song speaks volumes to all of us who are in music ministry.
My wife and I love to listen to Matthew West's "Only Grace", and I am partial to 4Him's Psalm 112.
When it comes to a more classical sound I have always enjoyed Tito Schipa who was an operatic tenor back in the 40's and 50's? I think.
My mom always listened to Doo Wop and hooked me on it at a very early age, but then she also liked to listen to Mario Lanza who portrayed the greatest tenor of all time: Enrico Caruso.
I've been told that I sound like the great Irish tenor Frank Patterson (no relation)
and Andrea Bocelli as well. Both which I enjoy and take as quite a compliment considering that I have not studied voice in about 8 years; yikes!
I hope I haven't written your ear off ...
Peace to all,
In Christ,
Darrin