As others have said, New Haven reigns supreme. In particular, Modern is my choice.

That being said there are plenty of contenders. I grew up on Wooster St so Sally's and Pepe's will always hold a place in my heart but Modern, and honestly Bar, are the kings. Little Rendezvous in Meriden and Hometown in Wallingford are solid if you're in the area. Joey's in Hartford is great. It really just comes down to your preference but I've never once been recommended a pizza joint in Willimantic. I'll have to check em out.