the Black Pearl in Newport has arguably the best,personaly i think it is the best!!its not "guy fieri style".its classic sit outside among boats and tourists new england kinda style,with great chowda!!
We did a food tour through Pikes Place Market in Seattle. One stop served Clam Chowder which they said was the second best in the US. They told everyone that the best Clam Chowder in the US was at the Black Pearl in Newport. Can't get a better recommendation than that.