Whitney Houston was the master of melismatic singing, which is not to be confused with vibrato.
Melisma is the suble multi toned sounds produced on a single note like she did most famously on I,yi,yi, will always love you, oo oo. When done well it is like a ripple across a note of music, with very small variations upon that note.
Whitney could also do the most fluid runs from deep in her diaghram all the way up into head voice with no break in the clear tone of her voice. And she could do them in reverse too! She used runs and melisma both tastefully and meaningfully when singing. She sang from her heart and did not do vocal gymnastics for effect only. She grew up a gospel singer and was anointed by the vocal gods. This sound became more prevalent in her singing when she broke free of the whitebread pop princess image that she was packaged as by Clive Davis.
The most famous use of melisma in popular music is Mariah Carey's "Vision of Love", where barely a single note is sung as a syllable and she riffs and trills and glistens on everything. It is astonishing, but not everyone likes it. And she does it way too much.
Jennifer Hudson is not as vocally gifted but way over utilizes runs and has a very unpleasant "screaming" tone to her sound when she puts the gas on and adds power to her voice. I am not a fan.
Christina Aguilera is also a great one to over indulge in these techniques at times, where the vocal sounds can blot out meaning, and lyrics are secondary to the tricks. Yet they are all arguably soulful. Aguilera actually has a higher range than Streisand, in that she is a soprano and yet the timbre of her voice is smokier, so it seems deeper.
Celine Dionne is the most influenced by Streisand, hitting soaring high notes with a thin and very precise vibrato. It is most about the precision placement and she is a very studied singer. She has a gorgeous, slightly nasal voice like Streisand but lacks in musical interpretation and spontaneity. She has said many times that Whitney is her favourite singer.
Mariah and Celine have the largest ranges, with Whitney and Christina both having larger ranges and more powerful voices that Streisand. Houston's voice is undoubtedly the most powerful and at her best she does not have a weak spot in her range. It is not hyperbole that she could easily have sung opera with training.
What I am trying to say is that many singers have been compared to Whitney Houston, but Whitney Houston has been compared to no one.
She sang from her heart with amazing skill, instinct and an unmatched voice. Singing is a measurable talent, even if our tastes are subjective.
If you think they all sound the same, or tend to use the word 'caterwauling" then there is usually some discomfort with black singers going on to put it politely. (Patti Labelle caterwauls if you must use it.)
Whitney could sing pure noninflected pop any day but she had too much talent and soul to not show off sometimes. NO one sounds like Whitney Houston. Nope.