"The best" is a matter of interpretation, and may differ from person to person. The first few pages of this thread provide an in-depth analysis of most different types of earplugs, and their attenuation (noise reduction) varies depending on how they fit.
As for me, I've bought standard musicians earplugs, and have been fitted by an audiologist with both custom solid and musicians earplugs. None of these provided enough protection for me, so I always use HEAROS Super Soft foam plugs, which are rated NRR32, the maximum possible attenuation without using external earmuffs.
Downside, as mentioned, is that attenuation of higher frequencies is greater than lower ones. You won't hear as many of the high notes in the music, but for me there was no other choice, so I got used to it.
Some of my friends use the standard ER-20 musicians' earplugs and are satisfied with them, and others have been custom fitted with musicians' earplugs and are happy with them as well. The key to me is fit: If the earplugs don't seal properly, they are much less effective. I recommend trying some different ones out and deciding what works best. I've spent a couple hundred bucks going through this process, but we only get two ears (if we're lucky), and hearing is priceless...it's money well spent.
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