But from reading experiences in the forum, I got the idea that different branches of the story are mostly traversed by choosing between good and evil, not so much race or class. But I might be mistaken...
While certainly there are major plot points where important decisions shape the story's future, there are a lot of dialog reactions and options unique to races and classes. Every now and then, one of these unique-to-the-class/race is a real gem.
The early game experience of a tiefling is entirely different than that of a gith, even if the decisions are substantially similar. Especially from a role playing perspective, you might be looking at the same events unfolding, but from behind entirely different eyes.
For myself, I usually just start playing with some idea, and maybe I'll play all the way through and maybe I won't. If I reach a point where I think a different idea would be more fun or more interesting, I'll scrap the current idea and start again with the new one.