I've bought a lot of fabric from Keepsake Quilting, and have been very pleased except for one fabric, and I'd bought 4 yards of it. They took it back, no problem, no questions, and refunded my entire amount. That gives me confidence that should I run into any other problem, I'll receive the same, terrific customer service.
Having said that, I also love Connecting Threads, Thousands of Bolts, and Fabric.com. I also have relationships with two sellers on eBay, one who deals primarily with Red Rooster Fabrics, and the other who has a lot of different fabrics but she only carries the best. I only buy from those two sellers.