Paul was the better musician, was a bit more professional, and had more of a knack for the business side of things. When someone asked John if Ringo was the best drummer alive, he said "Ringo isn't even the best drummer in the Beatles", as Paul was a very capable drummer. Paul was so good that when they needed a bassist, he switched from guitar to bass and ended up writing amazing bass lines (like Rain, wonderful stuff) and being famous for that, even though he was primarily a guitarist. He wrote some great melodies, too. Some of the best love songs came from Paul. John had a problem remembering lyrics and chords in the beginning, and was jealous that Paul was so good (they were only 15/16 when they met.) but Paul taught John some stuff.
John was more of a revolutionary; he wrote more open ended lyrics, and wasn't as much of a cliche. He sort of opened the door for the "introspective, contradictory" rock star, one minute being a lazy asshole, the next being incredibly kind hearted and hard working. He had the better sense of humor between the two, and would bring that "Beatle wit" that made them so loveable in interviews. He had a much more distinctive voice, and wrote songs that were way ahead of their time, like Tomorrow Never Knows, Across the Universe, Yer Blues, etc. He was known as the druggie of the band, but he had only taken LSD a few times - it was Paul who became a life long stoner, and kept taking LSD for years after the rest of the band quit. John did have a problem with heroin for a bit, but quit. I think John was the prototypical rocker who paved the way for grunge, and did things long before guys like Cobain were born.
Paul obviously had the longer career, but John is still considered one of the biggest rock and roll icons and legends to this day, with a fraction of the career that Paul had.
I'll go with John on this one, but it's still close - they both brought their own style to the band, and both would have been nothing without the other. The Lennon/McCartney brand is still the greatest songwriting partnership of all time, IMO. Overall, the Beatles were a monster, though - they were so good, that even George started writing number 1 hits and became an amazing songwriter in his own right. All of the talent of Lennon/McCartney rubbed off on him over those years. Both wrote songs for other bands - David Bowie's first #1 hit (Fame) was co-written by John Lennon, as well as "Whatever Gets you Thru the Night" being a major hit for Elton John.
