It's definitely Please Please Me for me as it was the first Beatles album that I ever heard and the first vinyl record that I bought by The Beatles. I think it opened my eyes for all the other wonderful music and bands of that time period and it was a great comfort for me during tough times at school. It also made me happy when I felt the most useless.
That is, overall, a happy album! Welcome!
Mono Sgt Pepper and the US Yesterday and today & Hey jude album
The Red & Blue albums were my introduction to The Beatles and music in general when I was 2 years of age. I haven't looked back 42 years later. After learning of their history, Abbey Road means a lot to me for the simple fact that they bonded together one last time to make a fantastic final album.