Ummm, wow. Both of them were super unimpressive aside from Durability which I would side with Destroyer kinda since it was its own power and Mjolnirs that blew it apart. Doesent mean it was destroyed.
Thor obviously has and had been holding back since he doesent want to vaporise his own treammates and the city.
Thor never even got to hit Ultron. But the last fight in the city was so freaking underwhelming...Ultron never felt strong. Just durable.
Anyway, Destroyer ftw