Go for the American!
I learned to sail on an American 14-6 about 10 years ago. It is BY FAR the MOST stable 14 foot boat around (aside from a catamaran).
The 14-6 can be singlehanded with ease. I've sailed it with my two toddlers aboard. I was able to manage both boat and toddlers safely in modest conditions.
I imaging that the larger version (American 18) would by more stable that the version that I learned on.