I use Argan Oil and love the softness from that; I have never used Castor, even though I have a bottle that has been sitting there for over a year. tsk tsk
I don't think my hair is picky. Every oil I have tried has worked.
olive
coconut
castor
avocado
wheat germ
I currently use olive (penetrates hair shaft), coconut (penetrates hair shaft), and wheat germ (vitamin e and ceramides).