Both are my favorites singer-songwriters! They are incomparable of what they do... and have different styles of songwriting... I have great respect to both of them and their works!
Here's my explanation...
Bob Dylan - he is a great poet who happens to know music:) His writings are like parable stories... He is even idolized by the Beatles and Queen to name a few.
James taylor - Great folk writer who happens to merge rock-country-folk... and have great voice and unique style of playing guitars.
As a singer and guitar player, I like James Taylor better.
As a songwriter, I want to be like Bob Dylan.
As a plain listener, James has great tunes and has better voice ... more contemporary than Bob.