Lobster loving family was in town and we hit both spots in a 3 day period - having lobster rolls at both places. I've dined at both places several times but never within such a close time frame.
Apriori, I thought I'd prefer Neptune - unadulterated chunks of lobster drizzled with warm butter sounds decadent and is more aesthetically pleasing than B&G's mayo-based lobster mixture.
Bottom line: I prefer B&G - their lobster was much fresher tasting than Neptune's as well as there was a little shell in Neptune's mixture.
In this never-ending debate - my vote goes solidly to B&G.