I'm not totally sure if I have ever done a kit. I can't think of any and every quilt I can picture that I've made where the fabrics were pre-selected were BOMs. Does that qualify as a kit? None of the fabrics were pre-cut.
That being said I prefer to choose my own fabrics. I either really like a pattern and then find the fabric I want to use or, I find the fabric and then decide what pattern.
I do often buy collections of fabrics or pieces of a collection and combine it with another or with my stash. I have one planned that uses 2 jelly rolls of one collection and 6 fabrics from my stash.