shoulders
I only use a shouldered paddle. I like the feel of the edge in my hand, with just the thumb and index finger on the loom. I know where my hands are withhout looking. I never use a sliding stroke and have no issues moving the paddle around for rolling or bracing. Just personal preference.
The
shoulder makes a catch point that is easy to find.(and tends to fill the hand more)
Some like the shoulder for paddling in winter or colder times when using mittens. The loom length being correct for the user seems more necessary than a very low shoulder or a non shouldered paddle.
With no shoulder, the entire transition area (loom to blade) becomes the grip area so the width of the loom becomes almost non important.
neither shoulder style has much effect on a sliding stroke if the user is proficient with the paddle and the sliding stroke.
Best Wishes
Roy
Loom Length
Using the standard biometrics for building a boat and paddle (which is how this stuff got its start) will produce a loom that is about shoulder width and that places the hands, when held straight out, at about the inside of each gunwale. Good torso rotation will keep that hands from hitting the boat. That being said, this is just a starting point to figuring out what is optimum for each paddler. Some very strong paddlers (say, serious racers) these days seem to like a loom that is a bit wider than this.