I recommend mounting to the jack plate if you have one. Mounts are a little pricey, but if you are a DIY'er, you can fabricate one pretty easy. This raises the transducer just a touch and protects it more from stumps, trees, and rocks. It also saves extra holes in your transom. If you don't have a jack plate or want to mount to your transom, I also run a Champion and mounted as low as I could on the very rear of the transom, not the area near the drain holes. I also mounted on the port side of the engine and near the middle of the boat, not the edge. I did use a stern saver so I didn't drill directly into my transom. I don't think placement matters so much as long as you are happy with the picture you are getting on your electronics. I am sure others have better answers than I do, but this is my 2 cents.