my impression after a bit of reading and talking to an expert is that the foam-type plugs actually provide the best protection, but at the cost of shitty sound because they have a low-pass characteristic (with >10 dB attenuation difference between subbands). The "hi-fi" type plugs sacrifice some attenuation for a more or less flat frequency response.
My take on it so far has been to err on the safe side and live with the shitty sound. Especially since hearing loss usually starts with the high frequencies, I rather put all the attenuation I can get on the highs. On the German market, I've found Hansaplast plugs the most comfortable and effective, plus they even got a lot cheaper recently if I'm not mistaken.
Of course the choice of earplugs is also a function of how sensitive one's ears react to noise. As a musician, shitty sound is hardly tolerable. But for me as a consumer, I usually am more concerned about the DJ putting on good records, rather than caring about a slightly muffled sound.