Now I'm torn here, that's one influential album everything from concept to cover and it stands the test of time like not many other 60's albums.

But I think the greatest influence is not the songs, as good as they are, but the sound and production and to me Sgt Peppers is so obviously influenced (particularly by Lennon) by Pet Sounds which came out a year earlier, only they took it a step further by introducing stereo panning to their sound. Saying that Sgt Peppers whilst a band album is so clearly influenced by McCartney who I don't think was so influenced by Pet Sounds.

Personally I prefer Sgt Peppers to Pet Sounds so that's no contest for me, but as for the more influential...I dunno

Cheers
Mike