Over the years, I've use solids from many manufacturers. In addition to Kaufman's Kona Cotton Solids and Moda's Bella Solids, I've used Marcus Brothers Centennial Solids, Northcott's ColorWorks Premium Solids, P&B's Colorspectrum Solids, and RJR's Cotton Supreme Solids. I think the only major manufacturer I've missed is Michael Miller's Cotton Couture Solids and that's mostly because it's not carried locally for me while all the others are (I also think the collection name is just a bit snooty, but perhaps the fabric lives up to it).
The OP only asked about the Kaufman and Moda lines, but if I had to choose just two out of the six with which I have experience, they would be RJR and Marcus Brothers, in that order. Both have been exceptional in every way for me and are limited only by colors available (RJR has 150, Marcus has 58).