Talk to the Bloc Loc people and ask them the most popular size that follows most patterns on the market of quilt making. I did that and the rep at the quilt show advised me which ones to buy. I have been very happy about my choices and have not needed any more.
Everyday use rulers, I use the Creative Grid because I can see the markings clearly, from the 6" ruler to 28" with a 'lip' on it. I am blind in one eye, and this really helps to be more accurate in cutting. Taking extra care the time to cut it right the first time saves time and money. I have learned so much on QB to be a better quilter and still learning at 76 years old.