We may be able to do both (in September) but, if need be, which one would you choose? Thanks for your advice.
I’ve not been to Bulnes. My visit to the Picos was one of the highlights of a trip to northern Spain. Staying at the Parador de Fuente Dé was wonderful as was the cable car to the mountain top.
I choose Fuente Dé, it's easier to get to and has better infrastructure. Though in the summer months the line to the Teleférico can be quite long, better to get there early or stay in the next door Parador.
I love Bulnes, but wouldn’t stay there. I am not sure there are more than one or two lodging options there, and you are probably going to have a bit of a walk from the funicular. I’d suggest Las Arenas de Cabrales instead, you can make an easy day trip to Bulnes from there (less easy but very doable if you hike instead of the funicular). There are quite a few lodging options and restaurants in Las Arenas. Las Arenas has more options than Fuente Dé.
I’ve not been to either. However if you are staying closer to Covadogna and thinking that the drive to Fuente De is going to be 90 minutes or so, you may want to cross check vs google maps drive times. We were staying near Posada and planning to do that but because of construction (June 2024) the drive times during the week days were showing as 2.5 hours.