Kona is my favorite, and is the one I buy by the bolt when I can get a good deal.
Moda is also good but the fabric is softer off the bolt and for me this makes it a little harder to work with.
Connecting Threads solids are also good but some of the colors look a little "muddy" to me when I compare it to Kona - sometimes that's a good thing, though.
I also agree that getting a color swatch card for each line is a great idea. I wish CT had a color card for their solids.