Like most everything in quilting, it all depends on the look you want and what the quilt is going to be used for.
If it is a quilt that is going to be used and loved, then piecing your border isn't going to matter much. Even if the "print" doesn't match, is that going to make the quilt any less loved??
If you are making a quilt to enter into a show, and want to win a prize, then find out what the judges look for in a quilt and the borders. Do they want to see a continuous border?? If so, then DO NOT PIECE your border, or you will lose points.
I think too many people get stuck on doing things the "right" way. If you are not making quilts to enter into shows, then doing what you want, with the fabric you have IS the "right" way. Do you really care if your borders are a bit wavy if the quilt is going to be used by a toddler and dragged around on the floor? Is the quilt going to be used in a teenagers room, and do they really care if everything is "perfect" on the quilt?? If you are making a quilt that is going to hang on someones wall, then wavy borders may distract from the quilt, and you will want to do them differently.
The question you need to ask yourself, is how much of a difference, in the overall look of the quilt, and what it is going to be used for, will make in the way you do your borders.