I have all 4 rulers, and a Janome 6600. i was asked by my LQS owner to learn to use them and demo them at a recent shop hop. I found Slim and Archie most useful. Slim is great for long straight lines and works great 'Dot to Dot' quilting and straight lines and ditching. Archie was a favorite of mine because the bottom, smily side is designed for the arcs in 2 inch squares, and the cathedral arch of the top side of Archie is a difficult shape to stitch free-hand because of the need to do a mirror image to get an even arch.
As far as the others are concerned, Squiggy is great for serpentine lines, and curves, but they just weren't as easy for me to master in the short time I had to create samples for the Shop hop. Shorty is fine for straight lines, too, but maybe not as universally helpful.
Hope you've found my feedback helpful. I'd get both Slim and Archie...