Having researched multi-genre games, I am now wondering how to best utilize this feature. Take, for example, airplane and racing games - their favored genres are simulation and casual, which are the opposite of each other. If I want to make an airplane game, should I make it purely simulation or casual, simulation+casual or simulation/casual + something else? Will having 2 bad genres be worse than 1?
You can look here for a table that lists good Topic/Genre combos.
Here is a list of genre combos and the appropriate weights you can give throughout the development phase.
The first genre chosen is weighted twice as much as the second one. Say you picked one bad genre and one good genre; if the bad one is first you will be worse off than if the good one was first.
You can also see that the first genre you choose changes the optimal weights throughout the development process. I would suggest choosing the first genre based on the strengths of your characters.
Here is an excerpt from the wiki about how to use the tables.