Previous answers cover the the practical side. I would add that your choice depends on what are you expecting from this walk. If you want to start and finish, and the certificate on your wall, so León-Compostela it is. Ditto if you are looking for a good time, meeting lots of people, having fun (nothing against it...) On the other side, if you love forests, old monuments, picturesque villages, prefer Roncesvalles-Burgos. For more sober, soul-searching pilgrimage, include the Meseta between Burgos-Leon, or opt for alternative ways, other than the Frances.
The other point you should consider is dates, not only for the weather, but also bcs the "general feeling" changes. Summer is more relaxed, social, and there are more students on vacations. Spring and Autumn are quieter and more lonely; the average pilgrim is older, I think, with more "just retired" people. Winter...well, beautiful, but it is really tough.