Wow, that has changed over the years. At one time I would have said Abbey Road. Then The White Album was my fav for a long time but if I would have to pick today, I don't know. Rubber Soul, no Revolver. If I have to choose my all time favorite it would be Sgt. Peppers. That album changed my understanding of what rock music can be. Although it is the maturation of the process that began with Rubber Soul it still is the gateway album to what we call classic rock today.
Because Phil brought up the Stones and today is Mick's 75th and the local listener supported radio station is giving me 24 hours of the Stones I have to say my attitude toward them is the same as Phil's towards the Beatles. Where I've owned every Beatles record from Sgt. to Let It Be the only Rolling Stones I ever owned was probably everybody's least favorite and most unstone like Their Satanic Majesties Request. My favorite Stones is Beggars Banquet, no Let it Bleed, no Beggars Banquet.