The
Camino Frances is the seminal Camino route. Most other routes intercept and run co-terminus with the Frances at some point. A few Camino routes, like the Portuges and Norte do not. They approach Sanitago de Compostela from different directions. So, if you look at a map of all camino routes, the
Camino Frances appears like the spine of the Camino in Spain.
In any event, the
Camino Frances has perhaps the best infrastructure to support pilgrims. If you are doing your first camino, or suspect this may be the only time you will be able to do it, I recommend the
Camino Frances. As regards distances, you can go for the full course menu and start in southern France at St. Jean Pied de Port. From there you cross the Pyrenees into Spain, stopping at Roncesvalles. Many Spanish folks start their pilgrimages at Roncesvalles, or at Pamplona.
It does not matter where you start. The sole requirement to obtain the Latin Compostela document from the cathedral authorities at he Pilgrim Office is that you demonstrate that you walked AT LEAST the last 110 km from Sarria. You show this by presenting a pilgrim "credencial" containing at least two stamps per day starting at Sarria. Before Sarria, a single stamp per day is adequate.
You can obtain a credencial from your local / national Camino fraternal group. If you let us know where you live, someone will surely provide you a link to that group. You can also obtain a credencial at pilgrim offices located at major starting points, like St. Jean Pied de Port.
I hope this helps.