Single or double?
How do you like it? Single or double?
Well, depends on what are we talking about... Scotch? Take downs? Girls?
Not so interesting, but equally important, we are talking about mouthguards (aka gumshields).
These are the most important piece of equipment that money can buy.
I do not like to use protective equipment. At all. But the truth is that mine saved my teeth a couple hundred times.
I hate to wear it because it messes with my breathing (and with my kiais), if it falls down I need to wash it abundantly before using it again and it gives me a weir feeling in the mouth too.
But I use it every time I spar.
And I also hate gloves!! It gives you a completely false feeling about what are you hitting, with what part of the hand are you hitting and deceives you into thinking that you are punching correctly.
For Kyokushin, I never wear them. For Shotokan, I do not wear until I am forced to. In MMA training they are mandatory, but I still do not like them.
Of course, I do not complain when I box, because boxing gloves are part of the sport of Boxing.
Shinguards? No way!!
I prefer to bruise my shins that to protect them. Why? Because shinguards make my kicking unthinked. I do not need to mind really much about kick placement because my shins and feet are protected. Since my goal is self-defense I need to be aware if I am kicking an elbow or a knee.
I can not just careless kick and hope to make it magically land on a weak spot. I train for it to happen.
Cup? Well, I also was against it until I started rolling with brutal people who use their knees to pass my guard. Not I can not live without it (but I still hate it).
So, single or double mouthguard? Single will protect the upper teeth only but offers better breathing than double. Double will protect more teeth but will restrict your breathing even more.
But if you practice one of those no contact game while you wear a gi then feel free to do not use anything for protection. You don't really need it. Only people who want to learn how to fight needs it.
But the more you use, the less real it becomes but the safer you will be, and that will allow you to come back to training more often because of a reduced injury rate.
Too many choices...