Things to keep in mind.
1) Just about every boat North of NY/NJ will be a 6-Pack. They are Taxi's only, Don't expect showers, toliets, lunch, compressors, lots of space, etc.
2) With very few exceptions, The Dive boat season is from Mid-late May through late October. Heather and Dave's boat the Gauntlet in MA and the Atlantis out of New London are the only two boats that come to mind running this winter. Cape Ann Divers may also have one running.
3) Most of the boats have a fairly standard set of wrecks which are within 20 miles of port. If you want to branch out expect to have to do your own charter, or find frineds with a good boat.
4)In the summer, Expect to loose 1/3-1/2 of your weekends to weather. In the winter expect it to be a crap shoot every dive day.
5) Northeast boats anchor, don't expect to do any drift diving. This means jon lines for the up line when the current is running. Remember, FOG happends, don't be a search target in a 50 foot Nantucket Fog.
6) The water temp is colder North of the elbow of Cape Cod. Cape Cod Bay is always cold
7) Good vis is anything over 15 feet.