I too recommend Kaserna. It is not donativo anymore. 18 euros, with diner and breakfast included. Kind hospitaleros. In the current circumstances, you need to check previously if albergues are still open.
There are tons of info in this forum about SJPP and both routes; use the search function, as above mentioned.
The Napoleon route is the generally preferred, It is tough, but with breathtaking, unique views. The Valcarlos option is easier, more gradual (but with some steep sections, anyway), and much less crowded. It goes by farms, villages and woods (with a bit along a highway).
I enjoyed both routes. Basically it is up to your preferences, confidence on your fitness level, etc.
I stayed in the municipal albergue in Valcarlos; it is very comfortable, with a kitchen. It is a lovely Basque village.