I have a Stitch in the Ditch Ruler that I love. I bought it right after I got my machine and it has become a part of me. The problem is as much as I love my ruler I know that I can't get another one. The company that produced the ruler went out of business. My favorite ruler is the Itty Bitty by Off the Edge.
I love the size, shape and easy to see color. It is marked with quarter inch registration lines and 45 degree lines. It also has the tabs that you line up with your ditch and put your needle in the correct place.
Notice that my thumb and third finger can comfortably hold the edges of the ruler and my pointer finger can be use for control. I love this ruler and will use it until I loose it or break it.
Since I do A LOT of Stitch in the Ditch I know that I need a back up ruler. I have tried a couple, but the one I like best is Deloa Jones' Little One.
It is clear which makes it harder to see int he picture and harder to see if I lay it down on the quilt. That is the downside. But it does have the quarter inch lines and 45 degree lines. It has the off set tabs.
It is little bigger then my Itty Bitty, but it is still very comfortable to use. My only really wish is that it was not clear. And I will just have to get over that.