I get a lot of confusion from my beginner students every year. There are many kinds and shapes of shoulder rests. Let's talk about the most common shoulder rest you will see in the shop. (If you want the conclusion, jump to the end.)
1. KUN violin shoulder rest.
If I had to guess what kind of shoulder rest a violinist uses, it probably is KUN. It is probably the most popular shoulder rest you will see. I have tried a lot of shoulder rests in my twenty years of playing, looking for the perfect shoulder rest. Guess what I am using now? A KUN.
Here is why I choose KUN, and why I recommend it.
1. You can find it easily in most music stores.
2. It is comfortable, durable and reasonably priced.
3. It is shapes to fit most people, which I think is the reason why so many people choose it.
You can adjust the height and width of the KUN shoulder rest, but obviously one size doesn't fit all. What if you have a shorter neck than most people, or you just prefer a much flatter shoulder rest?
2. Playonair shoulder rest
During my journey for the perfect shoulder rest, I decided to try a shoulder rest that can adjust to the shape of my shoulder. I tried Playonair for less than a year and went back to KUN.
Why I didn't like it:
1. I had to inflate it every time I played.
It is an air-inflated shoulder rest. At the time, I was practicing up to 3-4 hours every day. Playonair did not hold its shape during my practice, it slowly lost its air, and eventually became completely flat. I got tired of inflating it.
2. Playonair makes too much contact with my violin.
The body of the violin vibrates when it is played, which means any contact to the violin will diminish the vibration, and it will affect the sound quality. Compared to the KUN, Playonair covered almost 1/3 of the the back of the violin.
Needless to say, it was an easy decision to switch back to KUN.
3. A shoulder sponge
I have never used a shoulder sponge for an extended period of time, but my students usually receive some kind of sponge when they purchase/rent their violins.
A shoulder sponge is a little tricky. It comes in many shapes, heights and materials. You may have a sponge that is really soft and will adjust to the shape of your shoulder, or you may get a harder material that is more rigid.
I think a sponge is good for beginners and very young students.
It is easier to handle, and usually the cheapest option. If you are crafty, you can even make a sponge yourself that fits you better. I have made many sponges for my students, it is quite easy.
4. Bonmusica shoulder rest.
I have never used this shoulder rest before, but I have had students that use it.
I would never recommend this shoulder rest, because:
1. It is bulky
Most shoulder rests can fit inside a normal sized case, but Bonmusica has a very extreme shape. It is harder to fit in the case.
2. It is a little stiff.
I find the shape too rigid. The ideal shoulder rest should adjust to your shoulder. I find my students trying to adjust to the shoulder rest instead. It is never good news if you have to change your position because something doesn't quite fit.
To sum up:
I hope this helps you get started!