I want to chime in about stitch in the ditch also. For me, it's one of the most difficult ways to quilt with a walking foot! Requires a lot of concentration, and I am never satisfied with my ability to stay in the ditch (or keep an even distance from it). I like the idea of doing diagonals to avoid having to do SITD. Also, you may want to consider a more modern alternative, which is to use a walking foot to make wavy lines through the quilt. This is actually easier than trying to make straight lines as there is no "wrong" way to do it. There are a number of tutorials online, and you can Google "wavy quilting lines" and click on "images" to see some of the possibilities. I will link a few here:
http://sewsweetness.com/2011/09/back...and-other.html
http://bastingbeauty.com/2014/03/25/...wavy-quilting/
http://betteroffthread.com/2013/03/0...ting-tutorial/
https://sewfreshquilts.blogspot.com/...l-habitat.html