I should explain how I used the Ardco templates. I used the outside edges to cut multiple layers with my rotary cutter, then individually traced the inside edges to give me my hand-piecing lines. The most important for me were the corners.
If you are not planning to trace the sewing lines, then the acrylic templates might be better for rotary cutting. I had to be a little careful when rotary cutting with the Ardco metal templates to keep the blade angled just slightly away from the template. At first I wasn't careful and ran my rotary blade into the metal template once or twice. Acrylic templates would be thicker and would make rotary cutting easier; you wouldn't have to be careful not to run the blade over the template. However, with the acrylic templates you are not able to trace your sewing lines (unless you make another template yourself for that).
I suppose the ideal would be to get the Marti Michell template in your cutting size, and the Ardco cut-out template to trace your sewing lines.
Incidentally, the Ardco templates I love are the ones with the inner part cut out. I would not recommend their solid templates for the reasons cited above about rotary cutting with them.