Irena, as you know, I am still learning but I have always been very impressed with Handwriting Without Tears (which was developed by an OT). I have seen no research from them on Dysgraphia but they are one of the few handwriting models that promotes research. Personally I found the songs and methods helpful for my son.
There is a logic (with memorable stories) to the formation of the letters. They are grouped based on formation patterns. Capitals are broken in to 4 different strokes. Practice materials have raised borders which helps with the vision issues. I've seen the most success using their programs and methods. Before I knew Dysgraphia I was so impressed with HWT that I attended their training workshops to become fully certified in their program.
I would add that other handwriting methods introduce more opportunities for errors for those kids who struggle with reversals and can't "retrace" in the same space to move to the next stroke.
Hope that helps! I'm interested to see what else you learn.
