1. John Lennon was the greatest and the most gifted artist. His life was his music. He sang about his mother, wife, son, father, world peace and a lot of other stuffs. All of his Beatles and post Beatles works were purely guided by that artistic motivation. He was born to it.
2. Paul McCartney was/is the music man. Technically he was the most skilled Beatle. His melodies have stood the test of time. He was/is a happy going fun loving, melody man of great skills, probably incomparable.
3. George Harrison was a spiritual artist. He sought after greater purposes of life and gave music to his inner feelings and revelations in a rock era which was itself a challenging task to do. George lived a spiritual life of devotion towards what he felt was ultimate truth and played that tune and sang no matter what the whole world said or criticized.
4. Ringo can't be compared with John, George and Paul because his area was different from theirs. He is one of the most rhythmic drum players of the world. He is lauded by virtuosos for his simplicity and his rhythm style. So you could say he is pretty much talented too. So, there is goes. All of the four Beatles were competent in their own unique style. They honed their skills by years of performance in clubs prior to fame. That's why they were that good. Fame is another thing but no one can deny how good and artistic all of them were. They further developed their skills and art over the years during Beatles and the post Beatles era. &Rest is history!!!