Denser fishes like salmon and cod are the easiest to cook. You can overcook them, especially salmon, but they're both really delicious and generally easy to work with. I would recommend going with salmon for the extra flavor, but if you're concerned about over cooking, maybe cod instead.
Edit: I used this recipe, but with less dill because that's a crazy amount.
https://skinnyspatula.com/salmon-soup-lohikeitto/#mv-creation-223-jtr