Hi Karen .. good question but the answer (there is no real answer by the way) depends on a number of things - one is where do you live? If it is in Europe then the Camino is easy to get to, if not then it is expensive and if coming from far away there is that jet-lag time to consider.
Then there is "is this a one-off?" - if it is, do you want a Compostela? Then start ten days out from Santiago. If you will be returning in future years and have the funds and time to do that then start at "the beginning" of the Camino - I know, there isn't a beginning .. but the classic is St Jean to Santiago so you could start at St Jean and walk until you need to go home and return to that same point next year and move onwards.
If you are thinking of doing a couple of days here and there and jumping the gaps .. well, you could do that, but you would miss an awful lot .. what happens along Camino is that you end up more or less with a set of pilgrims who started the same day as you - jump ahead a few times and you will never make the connections, you will always be the new person - and you will lose a lot. Like changing schools every couple of days.
You do mention "which sections" so you may be thinking of that ... to me it isn't a good idea, but then, it is your Camino, not mine.
Then there is "what do you like?"- deep green hilly, often wet terrain - go to Galicia and walk to Santiago (start at Ponferrada perhaps).
Starting something new by climbing up out of one country and descending into Spain? Walk from St Jean.
The feeling of the medieval? big skies? Huge open spaces, not quite flat but gently folding? Dusty earth coloured villages rising up in the distance with sleeping dogs in the heat? Then walk the Meseta - Burgos to Leon.
You could even start in France and end in St Jean - beautiful soft country in France, but not many pilgrims so if you want the mass of pilgrims moving feelings then Spain is the place.
Oh! So many possibilities!!! Enjoy the planning!!