Anywhere around the west & south, I just love these areas the most.
Honestly, any place I haven't been before. I find visiting a new place is much more fun than going to the same place over and over.
Of the places I have been and wouldn't mind going back to are Boston and San Francisco. Both places you can easily get around without a rental car. (Though with SF you could rent a car for a day to visit the surrounding area.) Both have things to do for all ages. And both are known for their seafood.
I think I like Santa Cruz Beach and Boardwalk in California the best. Nice beach and water and lot's to do on the Boardwalk. Beautiful place.
My happiest vacations were spent in Yellowstone Park, WY, and at Big Bear Lake, CA.
Just spend a week in Madiera Beach last month. It's about 6 miles north of Clearwater Beach. Super cute little towns with lots to do, the sand/water were beautiful right there (we rented a condo on the beach), very quiet well maintained beach. We spent one day going to Magic Kingdom (about a 2 hour ride), but mostly just were beach bums and enjoyed the local restaurants. It was one of the more relaxing trips we have ever taken.. Especially with a 2 year old. There was so much to do that we canceled, didn't get a chance to do because we were just enjoying the beach that much.
I have a long list to go like Niagara Falls, Yellowstone, San Jose and some are repetitive places like Orange beach where i always get that peace and time to relax.