Having done both (from Lourdes), I would recommend going via SJPP
The Aragonès after Jaca is
very beautiful, and starting at Somport or Canfranc will always be very good options, but the walk up from Oloron to the Somport is often quite uninteresting, and it requires a fair degree of walking on tarmac roads beside heavy traffic -- parts of the Way between Canfranc and Jaca are also a bit meh.
The SJPP alternative is beautiful most of the way (of course nowhere near as spectacular as the Aragonès after Jaca), and it is also shorter, and easier.
The final direct comparison between the two is that the climb itself over the Somport is easier than that over the Bentarte, Lepoeder, and Ibañeta passes between SJPP and Roncesvalles.
If you are undecided about taking the Somport or St Jean route to the CF, you may wish to consider making that decision at Arudy rather than waiting until you reach Oloron. The priest with whom many people choose to stay at Arudy has route sheets for both ways, with the opportunity to save a day’s walk to Somport by missing out Oloron altogether + walking directly to Sarrance instead (28kms, maybe less). Buen Camino!
... but Oloron is quite a nice little town, and the best place to go for any last-minute supplies you might realise were needed after leaving Lourdes.
A great place too to look for a good French regional restaurant lunch, if you felt like one, in a far less rip-off touristy environment than Lourdes (which can be fine too, provided you know how to navigate a French tourist trap without getting trapped).