I prefer Mountain Mist Blue Ribbon 100% cotton batting for most of my quilts. This is the "old-fashioned" type of batting that antique quilts were made with, and requires close quilting (every 2") because it is not needlepunched or bonded. One reason I love this batting is because it gets softer with every washing.
I don't like Warm n Natural as well as the MMBR. WnN is needlepunched through scrim, and this gives it a stiffer drape. However, the needlepunching through scrim makes it extremely stable, so quilting lines can be 10 inches or more apart. Its stability makes this a great batting to use in wallhangings and for tied quilts.
I do not prewash fabrics, but I do test for colorfastness before using. The test involves dropping a small piece into water to see if any color bleeds into the water, and also rubbing the damp fabric against white fabric to see if any dye "crocks" (transfers).
The crinkly effect is expected in the type of quilts I make. If you examine antique hand-quilted quilts, you will notice that they are crinkly and soft. The puffy comforter look is a modern look. Also, if you do not want wrinkles, then it's a good idea to prewash your fabrics to eliminate any shrinkage and use a polyester batting (which will not shrink). This gives a different effect, with no wrinkles.
If you stitch around the edge of a quilt before attaching binding, and you have puckers from that stitching, that is a problem with fabric stretching. Starching fabric gives it stability so it is less likely to distort from cutting and handling. Using a walking foot also helps feed the layers evenly so you don't get puckering.