I have an affinity for Rhode Island. Newport is my favorite coastal New England seaport city. There are so many well preserved homes from 18th century colonial times near downtown, the waterfront and harbor are beautiful, Newport Bridge is a nice spectacle, and the mansions are probably the best example of gilded age opulence. Providence is a nice medium sized city well located between Boston and New York with an excellent dining scene for Italian, Seafood, and Portuguese food. It's also a premier college town with Ivy League - Brown, Johnson & Wales for culinary, and RI school of design for the arts. Block Island is my favorite Island, offering the tranquility and beauty of Marthas Vineyard without the astronomical costs and crowds. Plenty of attractive beaches on RI's south shore as well.
Overall I think Rhode offers a lot of the same amenities Long Island and Massachusetts could boast about, in a smaller, less crowded, and more affordable environment. It definitely is not without flaws though. Consistently high unemployment, famous for political corruption, and a bit of a strange accent (Good Will Hunting meets Linda from Coffee Tawk). Yes some of them do really talk like Peter and Lois Griffin.
I can't comment thoroughly on Long Island as I've only been on a few short visits. The eastern end of it is the best, Montauk is gorgeous. The Hamptons are a bit over the top, Newport is more inviting in my opinion. Western Long Island (Nassua County) didn't seem all that special, just a lot of mid 20th century suburban sprawl. Honestly I think New Jersey has more appeal, so does Rhode Island.
Block Island, RI is so nice I'm compeled to share some pictures
(http://www.flickr.com/photos/dpcsail/6075847413/ - broken link) by dpcsail
(http://www.flickr.com/people/dpcsail/ - broken link), on Flickr
Block Island North Lighthouse
(http://www.flickr.com/photos/27104981@N06/5391395741/ - broken link) by stp243
(http://www.flickr.com/people/27104981@N06/ - broken link), on Flickr
Block Island 2007
(http://www.flickr.com/photos/dangramm/2476692506/ - broken link) by Dan Gramm
(http://www.flickr.com/people/dangramm/ - broken link), on Flickr
Block Island Beach
(http://www.flickr.com/photos/trilbyyates/2652105653/ - broken link) by trilby_yates
(http://www.flickr.com/people/trilbyyates/ - broken link), on Flickr