It's between Revolver, Sgt. Pepper, and Abbey Road for me. All three albums are totally solid in every way. Least favorite is Yellow Submarine, as it had a couple songs that had been previously released, and then a bunch of George Martin crap no one cared about.
Also, George was totally the best Beatle, and it shows in his solo work. While Paul and John were both taking crap advice from their untalented wives, and making abortions of songs with Wings and disco albums, respectively, George was making the same music he would have been with the Beatles. While Paul and John together were great songwriters, apart they suffered, while George thrived. Lennon had some great solo stuff, Ringo had some great solo stuff, and Paul had like...3 good songs with Wings, I guess, but almost everything George did afterwards was amazing.