@ mrbitchdiva...

here are some opinions of voice experts:

Describing Aguilera's voice, singing teachers Phyllis Fulford and Michael Mailler said, "The low register is light and tired, the belting register is ample and full, but very scratchy because she screams; and head voice as well as whistle register are light, pure and bright. Her vocal range extends from G below middle C to C♯ one octave above soprano high C (G3 – C♯7). She can belt to F one octave and a third above middle C (F5). She possesses a good-sized technical arsenal. Her trill is solid, she has a big mastery of melismas, and can sustain very long notes."[162] Los Angeles Times writer Margaret Wappler adds Aguilera can deliver "a well-executed legato."[163] However, countertenor Philippe Jaroussky said: "She has no breath support and often sings out of tune. People say she can cover four octaves, but it's not true because below A3, the low notes are forced, unsupported, her belting voice is throaty and forced, for her highest notes she doesn't use head voice but falsetto or whistle register, they are disconnected registers. So, she can only hit good notes from A3 to B4. Her melismas are always show-off, they are almost never connected with the rhythm and the structure of the songs.

as you see, even expert opinions vary.