It's important to have the ones with all the subchannels. I was with a youth group in Washington DC a few years ago and some people brought ones with only 6 channels. It was a mess in that so many people were on these.
We own ones with the subchannels and have them set on my birthdate, then if that channel is busy we go to my husband's, etc. That way you don't announce where you are moving to the rest of the world (sometimes you want to ditch people who like to "listen in":
Example Oct 26 birthdate:
Main channel: 10
Sub channel: 26
This creates an easy to remember, obscure channel that, in most cases, no one else will be using. If they are, you announce that you should go to next agreed channel (which in our case would be DH's birthdate).