Both were two great songwriters in their own right, and they both made great songs. Personally I've always felt Paul was more melodic as a songwriter and especially as a singer, but John was more charasmatic and experimentive.
Some of John's Beatles songs:
- A Hard Day's Night
- Ticket to Ride
- You've Got to Hide Your Love Away
- Norwegian Wood
- Strawberry Fields Forever
- Nowhere Man
- Lucy in the Sky With Diamonds
- I Am the Walrus
- Revolution
- I Want You (She's so Heavy)
Some of Paul's Beatles songs:
- Fool on the Hill
- Can't Buy Me Love
- Michele
- Eleanor Rigby
- When I'm 64
- Get Back
- Blackbird
- Getting Better
- Yesterday
Fool on the Hill (Paul) is one of the greatest songs I've ever heard, but I could say the same thing about Lucy in the Sky With Diamonds. It's pretty hard to choose just one imo.
Although I think it's safe to say Paul was a much better singer and created better melodies.