That's up to you. The 40 degree edge will be more durable, but not quite as sharp. If your main use for the knife is to impress your friends with how easily it shaves your arm hair, stick with the 30 degree slots. If you use the knife for more demanding tasks like cutting up cardboard boxes and such, the 40 degree edge will last longer.
As others have said, 30 degrees is the goal at Spyderco, but they are sharpened by human beings using their own two hands, so sometimes the goal is met, and sometimes it isn't. I've yet to encounter one that was over 40 degrees, though.