I will address here the person who wants to build a stash to work out of. First of all, buy it when you see it, don't depend on it being there when you come back. With the price of gas and the shortage of time, why would you want to make two trips?When the quilt revival started in 1976 it was slim pickings. By 1980 the companies were really producing a variety of little calico prints. Around 1986 larger prints were introduced into the quilt shops. Many of your old prints no longer looked good with "new" stuff being offered.
Most people fall into the fat quarter or half yard category. This will work for you if you like a lot of different fabrics in one quilt. If you like the lightest color to be consistent all through the quilt, buy 3 or more yards of it. Borders cut in one piece on the lengthwise grain will take anywhere from 2.5 to 3 yards. Borders cut crosswise could take as little as a yard or as much as 2 yards.
The old rule of "if you love it buy 3 yards" works for some people. If you just need a little bit for fill in like orange or any little used color, buy just 1/4 yard of it. If you like quilts with just 3 colors you will need 2.5 - 3 yards of each fabric (minimum).
I believe in having a stash to work out of. Partially this is because I moved to a town that was 25 miles in any direction from the nearest large town. Also I like choosing the fabrics for a quilt at night, usually after 9 p.m., and can do it from my stash. I recheck the colors in the morning in natural light and I am cutting it before the stores open in the morning.
So, the answer really lies in the type of quilts you make. I know I like quilts with lots of fabrics in them so I know 1/2 yard will yield me 1.5, 2, and 2.5" strips with a piece left to cut into whatever shapes I want. I also know I could really get by with 1/4 yard and have none leftover.
If the comments suggest another post on this topic, I will do it.