While barrel length does affect range and accuracy its not all that contributes to it.
If you really want your BBs to go the distance, get a good quality hop up rubber.
Aside from the very front end the two guns and the 4 inch difference in inner barrels the two are essentially cosmetically the same, I would personally go for the 104 just because I prefer the look over the 103. You can buy either one, and further down the road if you decide you want a longer barrel then you can always purchase a new one.
"Its only a little bit on fire"