So let's see. We'll start with the Norte as I see Scruffy has not walked it and is painting a scary picture so I feel I must defend it.
July can be an issue on the Norte because it's high season and filled with beachgoers, but they are not staying in albergues dedicated to pilgrims. They will add to the de,and for beds in camping sites amd youth hostels, but those can be reserved ahead of time: La sirena in San Sebastian, the juvenil in Gernika como to mind as does the train station place in Llanes.
As for how hilly it is. I am no doubt overweight, and not just love handles. I have walked the Napoleon route and from there the rest of the Frances, I habe walked the Norte from San Sebastian to Llanes amd the Primitivo (the Portuguese central way as well, but that might as well be flat except for one bit out of Ponte de Lima). I have heard that the day out if Irun is tough, but you don't have to take the Alpinsta section. The rest ks just fine. The uphills are short, and not that terribly steep. Out of Zarautz there is also a way to walk via the coast rather than across the hill. The bit out of Deba is difficult, but you can stop in Olatz, breaking up the hike over 2 days.
On the Norte the albergues would fill up by the end of the evening, but you walked alone during the day. A perfect combinTion for me of a quiet walk and socialisation in the afternoon and evening. But if you are not a 40km walker who waltzes in late in the evening, and reserve in non pilgrim places, you will be fine.
Keep in mind that on the Norte you are likely to walk with a much greater proportion of Spaniards and other non English speakers than on the Frances. You decide if that is a plus or a minus for you. Also, on the Norte you will find a greater proportion of "hardcore" walkers, people who are members of hiking clubs, who regularly do have walking holidays, than on the Frances where many have just bought their first pair of trail runners (that was me, I now have a collection of them).
Great bonus for the Norte: scenary, excellent food, even in tyny villages, beautiful and important towns and cities (San Seb, Bilbao, Guernica, Santander, Santillana del mar and its Altamira caves). Back to food: nothing beats Basque food. Menu del dia in small places such as Ponema are a of outstanding quality and a much better deal than the pilgrim/tourist menu on the Frances.
Now, what it doesn't have that does Feances has:
A definite historial link to the birth of the Camino and the Middle Ages that permeates the Frances in its architecture, founding of towns ans cities, etc. Pilgrim mass is offered in many many stops, have not seen one on tne Norte, and once on the Primitivo.
Also the camaraderie of the Frances where you feel like a character in the "Cheers" sitcom everytime you enter a village, recognise faces and get a warm inviation to share a table while you enjoy a cafe con leche.
I feel these three things are what make the Frances the Frances, and there is a lot to say for those three things. I would venture to say that when people rhink of the Camino this is what they think of, rather than a long distance, inexpensive though stunningly beautiful walk through Spain, what the other Caminos are.
The Frances does offer many more choices of albergues, so if you feel like walking 5 km one day, that is possible on most days. There are very few 15km stretches without food, water or an albergue.
But it has a conga line of walkers, you will most likely always have one in view, in front or behind you. I don't mind them being in view, but I do mind hearing their nonstop chatter, but that is me.
It is said that there are times when there is a wave of walkers, an unusually large group of people moving together. If that occurs, it has been suggest you slow down and let is pass ahead of you, so that they keep fighting for beds, while you arrive as they are leaving, leaving you with a choice of beds.
As you may have guessed by now, I am not a fan of the pilgrim menu, but love the cafe con leche bar hopping. Food on tne Frances is not one of its best features, far from it.
So, now that we know the Norte is not anymore difficult than the Norte if you are able to walk the Napoleon route, that it is quieter, to the extent that you will most likely only meet other walkers in the evening, that both offer their own kind of beauty (scenery vs religious architectural heritage), that one offers a greater relgious/spiritual feel than the other, and that food is not a topic woth discussing on the Frances, you get to decide.
Ah, weather... in September 2013 or 14 when I walked the Norte, there had mot been any rain during the summer and I got 1 day of rain, record rain for that day mind you. Temps went as high as 34 degrees, so just as hot as the Frances can be (which is why you will never find me on a camino at the height of summer, bit that's just me).
Have a wonderful deciding which route to pick. Both will be rewarding, each one in its own way. Plus, once on one it's not as if you will ever be able to know how the other would have been like....