I am from that area and know it well. All 3 places are beautiful (also include mahone Bay in that trio) and right on the ocean. Lunenburg is a world heritage site. Downsides are very touristy and very small. Employment options are limited but many make a living there from tourism. I don't know if you are moving for a job, if so, not a worry. Housing is cheap especially compared to UK. You can get a big house with lots and lots of land for good prices. It is considered expensive by nova scotia standards because rich people from the US and other parts of canada often summer there and buy up cottages but I think it will not seem expensive to you being from the UK. Nova scotians are known to be friendly and down to earth. The heritage is very scottish/irish/british so you would feel comfortable. Like any small places, locals can be sometimes hard to break in but theses areas have alot of what is known as "come from aways" so they are adapting to change. Culturally, great in summer, lots of summer theatre and festivals, music etc. There won't be alot of restaurants, shopping options or museums etc. Schools will be limited and because it's rural, check out how long your kids will be on a school bus to get to school. You won't have any choice as to school, there will likely be just one or two. Crime, not a problem other than the usual local yokel stuff but nothing to alarm anyone.
Remember Canadian winters can be long and bleak and not much goes on (learn to ski, skate and curl and play some hockey and you will be fine. But these areas could feel isolated in winter, especially as you are not used to it. You are still only a 2 hour drive from Halifax but sometimes driving is tough during long storms so you can stuck at home.
Another town to consider is Truro ( less than one hour from Halifax) and bigger (not as pretty as the others) but more going on economically.
I would consider Halifax itself. It is fabulous, not too big but big enough that is has a few good museums, good theatre, restaurants, concerts and a hockey team, good hospitals and more choice of schools). Housing is still reasonable, and some places really cheap is you move outside the downtown centre. It has great parks, and good shopping and a more vibrant lifestyle. It is also on the ocean. Crime is more than the smaller places but not out of control.
It depends on whether you want an urban or rural lifestyle ( although most in canada do not consider halifax a large urban city). If you want to know anything else, I am happy to advise.