I did a couple of dives at Sandwich town beach (a.k.a. Sandy Neck) this summer, and liked it a lot. As someone else wrote earlier, very easy dive in terms of parking, entry/exit, and navigation. On one dive I came close to the stream coming out of the Canal and felt a drag. Great thing about this site is that you can dive it regardless of the tide. Seems like a popular place. I was the first in the water both days but upon completion of my dive 5-7 people were either in the water or gearing up.
I also did a dive with my kids at the Corporation beach in Dennis this summer, and it was a nightmarish experience from the beginning to the end. Unless high tide happens to be early in the morning on a cool weekday, I'll never come close to that place again.