The 26500 is the same size as a C cell, it's big. 18650s are probably the best value and they're longer and narrower, better for something that fits in your hand. However, if you build an
Evercool mod with two 14500s, you can greatly increase run time compared to a single 14500 without jumping up in size too much. You can do the same thing with two 18650s and get huge run time, but like using a 26500, it makes for a big mod.