I only use the 18350 tube when I know I'll only be out for about 12 hours, as the 800mAh battery gives me a good 6 hours of vaping time (I save my AW IMR 18350 700mAh batteries for my mech). If I'm going to be on campus all day until I go to work, I use the 3400mAh battery with the 18650 tube since that battery gives me well over two days of vaping time. While the smaller form factor is nice and easier to tote around, the size of either tube doesn't really bother me. If I know I can get away with using the smaller tube, I use the smaller tube.