I generally prefer a great deal of realism in my own escapism. I don’t see them as mutually exclusive. I want the world/universe and the characters inhabiting it to be internally consistent. I want the story to feel real to me. I don’t want to continually have to struggle to suspend belief as the story jumps the shark continually. My personal preference is thus for characters with a fixed sex. Furthermore I tend to find that characters whose sex is flippable generally have blander, more androgenous personalities than those that don’t since they need to be written in such a way that they can be either male or female.
For whatever reason, flippable sexual orientation tends to be less of an issue. I’d prefer that characters stay true to their orientation, whatever it is, and it’s hardly realistic to make everyone bi. Nevertheless I’ve generally found that most writers have satisfactorily finessed this to the point where I don’t usually notice it affecting the story.