Of course like everything else, what is best?
Are we talking the most convenient to use?
most comfortable?
most nrr?
most adjustable?
longest battery life?
most easily adapted to other uses such as with radios?
smallest size?
fit over big ears? (like mine)
most durable?
weight?
work well with rifles and/or helmets (low profile)?
position over or behind head?
use less expensive batteries (AA or 9V versus some of the little specialty batteries that cost an arm and leg, err ear)?
Note that even with some of the more expensive muffs, the smaller, lighter, etc. muffs tend to have less hearing protection and since the goal is to protect one's hearing, then the muffs may need or should need to be used with plugs for some applications. Since my Peltor ComTacs only have an NRR of 24, I wear plugs as well while shooting rifles and turn up the volume inside to compensate.