"HELP"!!! Because it would always send me right back to my happy place as a young Beatles fangirl in the 80's watching that movie on loop and playing the songs on cassette over and over and over and over again endlessly with my big sister.
Oh, no! Never hearing the other albums ever again would be torture, no matter which one I picked! (Can I still listen to the other songs with my iPod on Shuffle, at least? That can't count as hearing the album...) Normally I'd say Help!, which is my favourite, but I think I'll go with With the Beatles so that the Beatles will sound eternally young, simple, and romantic, with no experimental sounds whatsoever.
I can't picture myself listening to just one album for the rest of my life. I don't want to pick, but if I had to, I guess, I'd pick Rubber Soul. It's my favorite.