I think what's better might depend on the kind of quilting you prefer. I recently pulled a bunch of large floral prints from my stash along with coordinating fabrics, matched them with patterns and began making the tops, and I found that I wasn't as happy with these more spontaneous quilts as I've been with my planned quilts that spring from a specific idea or inspiration. So this leads me to believe that in the future, buying by project might be a better approach for me.
I think if you're a scrappy quilter, you pretty much need a stash.