I won't break down the exact issues because I think that these new remasters are probably the best but here's what I prefer when it comes to mono/stereo for each album:
Please Please Me: I've been mono on this one, but the songs I've heard from the new stereo master are really well done. But, I think mono is probably still the best because a lot of times you still get the voice separation.
With the Beatles: Not even close. Mono.
A Hard Days Night: Another easy choice for mono.
Beatles For Sale: I prefer the stereo on this one. The voices aren't as separated as other albums and mono mix lacks the fullness of the other mono releases.
Help!: Very close, but I like the stereo release. I like the vocals a little more in mono even though the stereo doesn't suffer from separation, but the instruments really shine on the stereo mix.
Rubber Soul: After two solid stereo albums, Rubber Soul takes two steps backwards in the stereo department which isn't surprising since this is the album that the Beatles started doing some studio experimentation creating a challenge to create a stereo mix on only four tracks.. But oh that mono mix is so, so good. If the whole world only heard this in mono it might just be considered the Beatles masterpiece.
Revolver: Still experimenting with moving things around in 2 channels and still failing miserably. Mono by a landslide.
Sgt. Peppers: If Rubber Soul took two step backwards, Sgt. Peppers took two more. Voices, handclaps, instruments seem randomly placed in one channel and it's especially annoying to listen to on headphones. Like Lennon said, you haven't heard Sgt. Peppers until you've heard it in mono.
Magical Mystery Tour: While not perfect, you can tell that they are almost there on getting stereo to work well with complex studio production. I could go either way here... some songs sound better in mono, some in stereo but if I was listening to the whole thing I think I'd choose stereo.
White Album: A lot of people think that the mono release was actually a fold down to please mono enthusiasts. Either way, mono is for collectors only because of the different mixes, the White Album finally gets stereo right and of course becomes the last album the Beatles release in both formats.
