That is kind of a loaded question. The NRR (noise reduction rating) dictates how many decibels will be reduced by the earmuff when worn correctly. In most cases, with muffs, the higher the NRR, the bulkier the muffs. What this means is that it will be hard to wear them correctly and get a good cheek weld when shooting long guns. Obviously when shooting handguns, it isn't the case.
What I have started doing is wearing the slimmer electronic muffs (Howard Leights or Walkers) and also wearing the cheap foam ear plugs at the same time. The hearing enhancement of the muffs make it easy to hear conversations even with the plugs in, but when shooting you get the benefit of double protection.
Not that you asked, but one of the most common reasons for flinching is noise (leakage through muffs).