Since just before X-mas, I have been using Peltor's ComTacs and find them to be very good electronic muffs. They are NRR at 25 which is better than most of the electronic muff competition. They run on a couple of AA batteries that are said to last for 250 hours. The circuitry is such that there are four volume settings and if you leave the muffs on by accident, they will shut off automatically and so your batteries don't die. If you have ever been to a class and seen either participants or instructors taking off their muffs and turning them off to save batteries, well that is an action you won't need to perform. There is no reason to remove the muffs and turn them off while you are at the range.
Regardless of the brand and rating of the muffs you buy, it is very essential that you wear plugs with the muffs to assure that you don't accidently get exposed to high noise levels due to leakage (hair, glasses, etc. will not all muffs to seat 100%) or because you have taken off the muff and some yahoo shoots. Well, at least you will have the plugs to prevent as much damage as would happen on exposed ear drums.
The nice thing about the ComTacs and plugs is that you can turn of the volume so that ambient sound is loud enough to penetrate the plugs and hence you can hear very clearly all the way down to leaves crushing under your feat, range commands not spoken loud enough to hear with muffs or a combination of muffs and plugs in place, yet not get hearing damage from gun shots that will not be broadcast in the muffs. Hearing range commands is very important and relevant.
The really nice aspect is that you are not as likely to get that accidental loud noise exposure wearing ComTacs because you will have no reason to take them off as many do in order to save batteries.
Oh, and the fold up quite nicely into a small ball.
The best price I found on these at the time was at...
http://www.shootersoasis.com/Hearing_Protection.htm
The people there were terrific.