So this is what I do - When it really counts and I want it perfect. Every border and every sashing piece is cut on the straight of the grain. I focus on two measurements for the borders ( only the middle of the quilt length and width). I do compare those to the edges and if one edge is more than 1/2 " too long I have been known actually run a line of stitching just inside 1/4" seam line for a short distance- it will actually ease some of the width in without pleats or ripples. I used this process for our Guild Raffle Quilt (42 squares made by 30 dif members ... none of them were the same size) and after quilting it was flat, square and no wavy borders.
Also if I know it will hang on the wall, I often will put a hanging pocket top and small one at the bottom. Then I have the hubby cut me a thin piece of wood to slide into the bottom one. Picture of my Christmas wall hanging.