I would suggest getting the EG 2.5's, I bought the EG 2's and they were huge on my face. A year later I bought the EG 2.5's and they fit much better. I wear a medium size helmet, and about a 7 1/4 size hat.
theoretically, spherical means your eyes are always through the lens perpendicular to the surface of then lens which means no distortion. none-spherical lens when you look away from the center of the lens, you are looking through the plastic at an angle. as a result it creates distortion.
I do notices my spherical goggles have clearer corner vision also they wrap around my face more so I can see more.
Regardless of which one you go with, make sure they fit your face well. If they don't fit well, they are more prone to having fog issues and at that point you simply cannot see, no matter what type of lens you have.