I have both and to me the Arrieta is better finished gun, internally and externally.
There are good values in the used gun market for Arrieta and AyAs and I think prices will drop more in the short to mid term. My Arrieta is an Orvis gun, the AyA a No. 2 and it has had issues, but I've used it a lot in Argentina.
I strongly agree with the posters who say the prices of new spanish guns are too high. Alternatively, I would rather have a good used Piotti than a new Arrieta or AyA.
Good luck in your search...