I would pit Jewel's voice up against ANY non-operatic female singer alive today, in range, power, control, whatever. She is my very favorite... because of that voice. Skeptics should watch and listen to her 2 performances she did while hosting Nashville Star this season (2007). Listen to them in digital quality, run through your audio system, not just the t.v. Friends of mine were over for dinner the night she sang one track. They weren't really country fans, or Jewel fans, but she blew them away. She also put a spell on the cohost. He was visibly amazed.
Jewel has at least 4 different tones she uses, and shifts in and out of from song to song, and sometimes during the same song. She has a little girl pouty sound, a Joplinesque wail, a deep-voiced, womanly tone, and an angelic falsetto from heaven. And she can do scat singing, as well. (E.g., Rudolph on her Christmas CD.) Jewel came of age as a folkie, but there is also country, blues, and rock in those pipes.
In my opinion, the best way to appreciate Jewel's voice is when she performs solo or in spare arrangements. Her second CD, Spirit, has a hidden track at the end where she does an acapella duet lullaby with her mother. Absolutely beautiful. On the same CD there is a track called Fat Boy. The lyrics are a little sentimental, but listen to what she does with that voice! In concert, I really get a kick out of her more personal songs... stuff where she wrote something on the road and where the band doesn't join in.
Only two wishes. One, that she had made it to the Johnny Cash-Rick Rubin recording sessions and had done a duet with Johnny (somehow Fionna Apple managed to make it), and two, that someday Jewel outgrows her tendency to wax overly-earnest in some of her lyrics. (I could be wrong on this last wish... if that's how the muse gets her inspiration, so be it.) Meanwhile, long live the Voice.