Having just rewatched these two films, I'd say that both are bad, but I'd give the slight edge to TASM2. It's not an easy choice, though.
Thor has the advantage in Loki. However, Loki doesn't steal the show as much as I remembered. Still a much better character than any one in TASM2.
I'd say that TASM2 has more scenes that are painful to watch. It screwes over characters like the villains, as well as Peter Parker himself sometimes. However, it has a few scenes that are somewhat enjoyable to watch. Watching Thor 2, I didn't find such low points as in TASM2. However, I didn't feel that any scene was particularily enjoyable at all. The whole film is extremely dull and almost all of the attempts at humour are ill placed. While Electro, Green Goblin and Rhino are terribly written villains, I at least somewhat enjoyed Electro visually. Whereas while Malekith isn't as terribly written (because he's basically a living plot point where there's not even any attempt to make him more interesting, which would mean taking some risks), he's so grey and boring that I enjoyed him less somehow. At least Electro expresses some kind of personality, even though he's dumb.