I would highly recommend the Portland area if you are thinking of moving to Maine. Portland has wonderful restaurants, a little more diversity than much of the state, it's right on the ocean, there are things to do, etc. Portland is also close enough to the lakes region to be able to swim in the lakes, camp, etc.
I wouldn't really recommend the Sanford area. I have never lived there myself (so you can take what I say with a grain of salt), but... it just isn't as nice as the Portland area (much more of a hick-like, closed minded feel).
Portland would most likely be more expensive than the Sanford area, but I think that you get what you pay for. If you decided to live in Maine full time, you would have more things to do living in the Portland area.
You should also check out South Portland and Westbrook. I would stay away from Falmouth, Windham, Gray, etc. They are all "nice" suburban towns, but you have to go closer to Portland to do anything.... and with the price of gas who wants to drive all the time?
I grew up in Windham and it is just plain dull. In the summer it is nice, because you can swim and spend time outdoors, but the winters are rough in the burbs... even if you like winter sports.
If you visit anytime soon, check out Portland. The east end is amazing.. overlooking the bay. The Old port is also great... like I said, some awesome restaurants... Yosaku (for sushi), street and company or Fore street (rated one of the top restaurants in the US) if you want something fancy, etc, etc, etc.
Portland kind of has a similar feel to Port Jeff on Long Island... but less ritzy and expensive.
Good luck!
