You can get a lot of different opinions on this.  if you read enough on here you will find that some people are really happy with 16% protein feed while others insist that you need 22% protein feed no matter what.  A lot of people are somewhere in between.  If you are raising them to show or have some other specialty reason you may need a certain one.  If all you are after is eggs the hens generally do OK on any of them.
The commercial egg operations feed 16% protein feed, or at least really close to 16%.  That is all they feed though.  They do not feed them treats and generally do not allow them to graze for forage.  If you are feeding a lot of low protein treats or if they forage for a lot of their food then a higher protein feed may suit you better.  
The commercial operations keep hybrid hens especially developed for egg laying.  Those hybrids are extremely good at converting feed to eggs.  If they feed a higher protein feed they will experience more prolapse and eggbound hens.  The more protein they eat the larger the eggs, the larger eggs can lead to medical problems with those small bodied hybrid hens.  Those hens still lay a lot of Grade A large eggs on that 16% protein feed.  
Most of our hens are not the hybrid commercial layers.  They are not that good at converting protein and other nutrients to eggs.  They generally have larger bodies and don't lay eggs that large for their body size.  They can handle a higher protein feed, especially if they get lower protein treats.  I don't know how you manage your chickens or what your ultimate goals are.  It is tremendously likely your hens will do great on an 18% protein feed.
For what it is worth I have dual purpose chickens and feed them a 15% protein feed.  They graze a lot and get treats such as low protein excess or waste from my garden.  My hens lay a lot of eggs.  They are not huge eggs but are a decent size.  Those hens hatch out a lot of healthy chicks and are themselves in good health.  I don't have prolapsed or eggbound hens.  I'm very happy with the results I get.