Don't know about "highest quality brand" on the market, because it's pretty much a given that if you want a quality mouthguard, the best thing to do is to hit up an Orthodontist/Dentist and pony up a couple hundred dollars for a fully custom-fit one (especially if you have orthodontic devices like braces).
Other than that, most MMAist and grapplers will use single pieces. From a plain/generic single, all the way up to the more price Brain Pads, you want to get one if you're in any type of contact sport. Myself, I've broken 2 molars grappling, but suprisingly never had any issues during stand up. In either case, even if I had a $2 generic from Big 5, it wouldn't have happened. You will probably only worry about a double if you are doing a lot of dedicated striking.
In either case, if you are thinking about competing you want to get one ASAP. Having a mouthguard in place changes the way you breathe pretty dramatically and you want to get used to that. I actually have 3 mouthguards myself (2 plain generic ones for regular training and drills, 1 Shock Doctor Pro for sparring). You can look at this page here
to get an idea of what's out there.
It doesn't matter if you agree or disagree
... As long as I don't bore you and I spark a moment of thought, my goal is achieved
Queng leon queng tigre ecu tacacut, queca pa? - Pampangan Mandarigma Motto