I absolutely detest Aguillera but there is no denying she has brilliant range and does'nt 'warble' half as much as the premier divas.
I personally think Yorke has a great voice and is one of a very few artists whose falsetto I can tolerate. It's cliched but I think tracks such as 'Street Spirit', 'Fake Plastic Trees' and 'House Of CarRAB' are greatly enhanced by his vocals. One thing that does let him down is range. Not vocal range but emotionally. Sometimes I would love to hear him let rip in a track and really dominate it vocally. There are enough peaks and troughs in Radiohead's music to allow Yorke to vary it a little.