The highest number or free staters per square mile is definitely Manchester, which is no surprise considering it's the most populous city in New Hampshire.
There are, however, free staters throughout the state. I suspect that each town will end up having a roughly proportional number of free staters when it's all said and done.
I recommend moving to the part of the state that best meets your needs in other aspects of life, such as job, type of geography you prefer, type of lifestyle, etc.
When you have an arrival date there are "welcome wagons" whereby free staters will be waiting at your home to help you unload your truck when you arrive. They make life much much easier. Just let us know in advance!
Good luck with your moves!