I tend to experiment often to see what pellet or chip flavors I like and what produces the best taste. Lol, like a mad scientist, I write down what I smoked and with what flavor profile so I can see what worked and what doesn't. Once you get to taste the difference, it actually isn't complicated to figure out what pairs well together.
Fish is alot more delicate than any of the other meats so it took a failure or two for me to decide which ones I liked best. My choices for salmon also depend on what seasoning I am using. Here's some options but remember, you'll need to figure out what tastes appeals to you as you go along.
Bourbon/ brown sugar glazed salmon- I use the bourbon barrel pellets, or pecan, or the pitmasters blend (which is hickory, maple and cherry)
Dill rub- the dill is it's own taste so you don't want to overpower, just compliment it so I found I liked pecan or oak best for it.
Lemon pepper- Apple pellets were my absolute fav.. but any of the fruit pellets I've tried so far seemed to pair well.
If I'm doing anything with some kick to it, like cajun seasonings or blackening rubs, I like a bolder smoke taste too.. I tend to lean towards hickory, mesquite, oak or I've been known to mix my own combos of pellets just to see what tastes good.
With that said, I'm guessing your going to be using the chips instead of pellets since this is your first smoke right? If that's accurate, go with apple. You can never go wrong with anything smoked in apple. lol
Hope that helps..